Tag QA

Testing Red Hat Enterprise Linux the Microsoft way

Microsoft and Red Hat logos

Pairwise (a.k.a. all-pairs) testing is an effective test case generation technique that is based on the observation that most faults are caused by interactions of at most two factors! Pairwise-generated test suites cover all combinations of two therefore are much smaller than exhaustive ones yet still very effective in finding defects. This technique has been pioneered by Microsoft in testing their products. For an example please see their GitHub repo!

I heard about pairwise testing by Niels Sander Christensen last year at QA Challenge Accepted 2.0 and I immediately knew where it would fit into my test matrix.

This article describes an experiment made during Red Hat Enterprise Linux 6.9 installation testing campaign. The experiment covers generating a test plan (referred to Pairwise Test Plan) based on the pairwise test strategy and some heuristics. The goal was to reduce the number of test cases which needed to be executed and still maintain good test coverage (in terms of breadth of testing) and also maintain low risk for the product.

Product background

For RHEL 6.9 there are 9 different product variants each comprising of particular package set and CPU architecture:

  • Server i386
  • Server x86_64
  • Server ppc64 (IBM Power)
  • Server s390x (IBM mainframe)
  • Workstation i386
  • Workstation x86_64
  • Client i386
  • Client x86_64
  • ComputeNode x86_64

Traditional testing activities are classified as Tier #1, Tier #2 and Tier #3

  • Tier #1 - basic form of installation testing. Executed for all arch/variants on all builds, including nightly builds. This group includes the most common installation methods and configurations. If Tier #1 fails the product is considered unfit for customers and further testing blocking the release!
  • Tier #2 and #3 - includes additional installation configurations and/or functionality which is deemed important. These are still fairly common scenarios but not the most frequently used ones. If some of the Tier#2 and #3 test cases fail they will not block the release.

This experiment focuses only on Tier #2 and #3 test cases because they generate the largest test matrix! This experiment is related only to installation testing of RHEL. This broadly means "Can the customer install RHEL via the Anaconda installer and boot into the installed system". I do not test functionality of the system after reboot!

I have theorized that from the point of view of installation testing RHEL is mostly a platform independent product!

Individual product variants rarely exhibit differences in their functional behavior because they are compiled from the same code base! If a feature is present it should work the same on all variants. The main differences between variants are:

  • What software has been packaged as part of the variant (e.g. base package set and add-on repos);
  • Whether or not a particular feature is officially supported, e.g. iBFT on Client variants. Support is usually provided via including the respective packages in the variant package set and declaring SLA for it.

These differences may lead to problems with resolving dependencies and missing packages but historically haven't shown significant tendency to cause functional failures e.g. using NFS as installation source working on Server but not on Client.

The main component being tested, Anaconda - the installer, is also mostly platform independent. In a previous experiment I had collected code coverage data from Anaconda while performing installation with the same kickstart (or same manual options) on various architectures. The coverage report supports the claim that Anaconda is platform independent! See Anaconda & coverage.py - Pt.3 - coverage-diff, section Kickstart vs. Kickstart!

Testing approach

The traditional pairwise approach focuses on features whose functionality is controlled via parameters. For example: RAID level, encryption cipher, etc. I have taken this definition one level up and applied it to the entire product! Now functionality is also controlled by variant and CPU architecture! This allows me to reduce the number of total test cases in the test matrix but still execute all of them at least once!

The initial implementation used a simple script, built with the Ruby pairwise gem, that:

  • Copies verbatim all test cases which are applicable for a single product variant, for example s390x Server or ppc64 Server! There's nothing we can do to reduce these from combinatorial point of view!

  • Then we have the group of test cases with input parameters. For example:

    storage / iBFT / No authentication / Network init script
    storage / iBFT / CHAP authentication / Network Manager
    storage / iBFT / Reverse CHAP authentication / Network Manager

    In this example the test is storage / iBFT and the parameters are

    • Authentication type
      • None
      • CHAP
      • Reverse CHAP
    • Network management type
      • SysV init
      • NetworkManager

    For test cases in this group I also consider the CPU architecture and OS variant as part of the input parameters and combine them using pairwise. Usually this results in around 50% reduction of test efforts compared to testing against all product variants!

  • Last we have the group of test cases which don't depend on any input parameters, for example partitioning / swap on LVM. They are grouped together (wrt their applicable variants) and each test case is executed only once against a randomly chosen product variant! This is my own heuristic based on the fact that the product is platform independent!

    NOTE: You may think that for these test cases the product variant is their input parameter. If we consider this to be the case then we'll not get any reduction because of how pairwise generation works (the 2 parameters with the largest number of possible values determine the maximum size of the test matrix). In this case the 9 product variants is the largest set of values!

For this experiment pairwise_spec.rb only produced the list of test scenarios (test cases) to be executed! It doesn't schedule test execution and it doesn't update the test case management system with actual results. It just tells you what to do! Obviously this script will need to integrate with other systems and processes as defined by the organization!

Example results:

RHEL 6.9 Tier #2 and #3 testing
  Test case w/o parameters can't be reduced via pairwise
    x86_64 Server - partitioning / swap on LVM
    x86_64 Workstation - partitioning / swap on LVM
    x86_64 Client - partitioning / swap on LVM
    x86_64 ComputeNode - partitioning / swap on LVM
    i386 Server - partitioning / swap on LVM
    i386 Workstation - partitioning / swap on LVM
    i386 Client - partitioning / swap on LVM
    ppc64 Server - partitioning / swap on LVM
    s390x Server - partitioning / swap on LVM
  Test case(s) with parameters can be reduced by pairwise
    x86_64 Server - rescue mode / LVM / plain
    x86_64 ComputeNode - rescue mode / RAID / encrypted
    x86_64 Client - rescue mode / RAID / plain
    x86_64 Workstation - rescue mode / LVM / encrypted
    x86_64 Server - rescue mode / RAID / encrypted
    x86_64 Workstation - rescue mode / RAID / plain
    x86_64 Client - rescue mode / LVM / encrypted
    x86_64 ComputeNode - rescue mode / LVM / plain
    i386 Server - rescue mode / LVM / plain
    i386 Client - rescue mode / RAID / encrypted
    i386 Workstation - rescue mode / RAID / plain
    i386 Workstation - rescue mode / LVM / encrypted
    i386 Server - rescue mode / RAID / encrypted
    i386 Workstation - rescue mode / RAID / encrypted
    i386 Client - rescue mode / LVM / plain
    ppc64 Server - rescue mode / LVM / plain
    s390x Server - rescue mode / RAID / encrypted
    s390x Server - rescue mode / RAID / plain
    s390x Server - rescue mode / LVM / encrypted
    ppc64 Server - rescue mode / RAID / encrypted

Finished in 0.00602 seconds (files took 0.10734 seconds to load)
29 examples, 0 failures

In this example there are 9 (variants) * 2 (partitioning type) * 2 (encryption type) == 32 total combinations! As you can see pairwise reduced them to 20! Also notice that if you don't take CPU arch and variant into account you are left with 2 (partitioning type) * 2 (encryption type) == 4 combinations for each product variant and they can't be reduced on their own!

Acceptance criteria

I did evaluate all bugs which were found by executing the test cases from the pairwise test plan and compared them to the list of all bugs found by the team. This will tell me how good my pairwise test plan was compared to the regular one. "good" meaning:

  • How many bugs would I find if I don't execute the full test matrix
  • How many critical bugs would I miss if I don't execute the full test matrix


  • Pairwise found 14 new bugs;
  • 23 bugs were first found by regular test plan
    • some by test cases not included in this experiment;
    • pairwise totally missed 4 bugs!

Pairwise test plan missed 3 critical regressions due to:

  • Poor planning of pairwise test activity. There was a regression in one of the latest builds and that particular test was simply not executed!
  • Human factor aka me not being careful enough and not following the process diligently. I waived a test due to infrastructure issues while there was a bug which stayed undiscovered! I should have tried harder to retest this scenario after fixing my infrastructure!
  • Architecture and networking specific regression which wasn't tested on multiple levels and is very narrow corner case. Can be mitigated with more testing upstream, more automation and better understanding of the hidden test requirements (e.g. IPv4 vs IPv6) for all of which pairwise can help (analysis and more available resources).

All of the missed regressions could have been missed by regular test plan as well, however the risk of missing them in pairwise is higher b/c of the reduced test matrix and the fact that you may not execute exactly the same test scenario for quite a long time. OTOH the risk can be mitigated with more automation b/c we now have more free resources.

IMO pairwise test plan did a good job and didn't introduce "dramatic" changes in risk level for the product!


  • 65 % reduction in test matrix;
  • Only 1/3rd of team engineers needed;
    • keep arch experts around though;
  • 2/3rd of team engineers could be free for automation and to create even more test cases;
  • Test run execution completion rate is comparable to regular test plan
    • average execution completion for pairwise test plan was 76%!
    • average execution completion for regular test plan was 85%!
  • New bugs found:
    • 30% by Pairwise Test Plan
    • 30% by Tier #1 test cases (good job here)
    • 30% by exploratory testing
  • Risk of missing regressions or critical bugs exists (I did miss 3) but can be mitigated;
  • Clearly exposes the need of constant review, analysis and improvement of existing test cases;
  • Exposes hidden parameters in test scenarios and some hidden relationships;
  • Patterns and other optimization techniques observed

Patterns observed:

  • Many new test case combinations found, which I had to describe into Nitrate; The longer you use pairwise the less new combinations are discovered (aka undocumented scenarios). The first 3 initial test runs discovered the most of the missing combinations!
  • Found quite a few test cases with hidden parameters, for example swap / recommended which calculates the recommended size of swap partition based on 4 different ranges in which the actual RAM size fits! These ranges became parameters to the test case;
  • Can combine (2, 3, etc) independent test cases together and consider them as parameters so we can apply pairwise against the combination. This will create new scenarios, broaden the test matrix but not result in significant increase in execution time. I didn't try this because it was not the focus of the experiment;
  • Found some redundant/duplicate test cases - test plans need to be constantly analyzed and maintained you know;
  • Automated scheduling and tools integration is critical. This needs to be working perfectly in order to capitalize on the newly freed resources;
  • Testing on s390x was sub-optimal (mostly my own inexperience with the platform) so for specialized environments we still want to keep the experts around;
  • 1 engineer (me) was able to largely keep up with schedule with the rest of the team!
    • experiment was conducted during the course of several months
    • I have tried to adhere to all milestones and deadlines and mostly succeeded

I have also discovered ideas for new test execution optimization techniques which need to be evaluated and measured further:

  • Use a common set-up step for multiple test cases across variants, e.g.
    • install a RAID system then;
    • perform 3 rescue mode tests (same test case, different variants)
  • Pipeline test cases so that the result of one case is the setup for the next, e.g.
    • install a RAID system and test for correctness of the installation;
    • perform rescue mode test;
    • damage one of the RAID partitions while still in rescue mode;
    • test installation with damaged disks - it should not crash!

These techniques can be used stand-alone or in combination with other optimization techniques and tooling available to the team. They are specific to my particular kind of testing so beware of your surroundings before you try them out!

Thanks for reading and happy testing!

Cover image copyright: cio-today.com

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Mutation Testing vs. Coverage, Pt. 2

In a previous post I have shown an example of real world bugs which we were not able to detect despite having 100% mutation and test coverage. I am going to show you another example here.

This example comes from one of my training courses. The task is to write a class which represents a bank account with methods to deposit, withdraw and transfer money. The solution looks like this

class BankAccount(object):
    def __init__(self, name, balance):
        self.name = name
        self._balance = balance
        self._history = []

    def deposit(self, amount):
        if amount <= 0:
            raise ValueError('Deposit amount must be positive!')

        self._balance += amount

    def withdraw(self, amount):
        if amount <= 0:
            raise ValueError('Withdraw amount must be positive!')

        if amount <= self._balance:
            self._balance -= amount
            return True
            self._history.append("Withdraw for %d failed" % amount)

        return False

    def transfer_to(self, other_account, how_much):

Notice that if withdrawal is not possible then the function returns False. The tests look like this

import unittest
from solution import BankAccount

class TestBankAccount(unittest.TestCase):
    def setUp(self):
        self.account = BankAccount("Rado", 0)

    def test_deposit_positive_amount(self):
        self.assertEqual(self.account._balance, 1)

    def test_deposit_negative_amount(self):
        with self.assertRaises(ValueError):

    def test_deposit_zero_amount(self):
        with self.assertRaises(ValueError):

    def test_withdraw_positive_amount(self):

        result = self.account.withdraw(1)
        self.assertEqual(self.account._balance, 99)

    def test_withdraw_maximum_amount(self):

        result = self.account.withdraw(100)
        self.assertEqual(self.account._balance, 0)

    def test_withdraw_from_empty_account(self):
        result = self.account.withdraw(50)

        assert "Withdraw for 50 failed" in self.account._history

    def test_withdraw_non_positive_amount(self):
        with self.assertRaises(ValueError):

        with self.assertRaises(ValueError):

    def test_transfer_negative_amount(self):
        account_1 = BankAccount('For testing', 100)
        account_2 = BankAccount('In dollars', 10)

        with self.assertRaises(ValueError):
            account_1.transfer_to(account_2, -50)

        self.assertEqual(account_1._balance, 100)
        self.assertEqual(account_2._balance, 10)

    def test_transfer_positive_amount(self):
        account_1 = BankAccount('For testing', 100)
        account_2 = BankAccount('In dollars', 10)

        account_1.transfer_to(account_2, 50)

        self.assertEqual(account_1._balance, 50)
        self.assertEqual(account_2._balance, 60)

if __name__ == '__main__':

Try the following commands to verify that you have 100% coverage

coverage run test.py
coverage report

cosmic-ray run --test-runner nose --baseline 10 example.json bank.py -- test.py`
cosmic-ray report example.json

Can you tell where the bug is ? How about I try to transfer more money than is available from one account to the other

def test_transfer_more_than_available_balance(self):
    account_1 = BankAccount('For testing', 100)
    account_2 = BankAccount('In dollars', 10)

    # transfer more than available
    account_1.transfer_to(account_2, 150)

    self.assertEqual(account_1._balance, 100)
    self.assertEqual(account_2._balance, 10)

If you execute the above test it will fail

FAIL: test_transfer_more_than_available_balance (__main__.TestBankAccount)
Traceback (most recent call last):
  File "./test.py", line 79, in test_transfer_more_than_available_balance
    self.assertEqual(account_2._balance, 10)
AssertionError: 160 != 10


The problem is that when self.withdraw(how_much) fails transfer_to() ignores the result and tries to deposit the money into the other account! A better implementation would be

def transfer_to(self, other_account, how_much):
    if self.withdraw(how_much):
        raise Exception('Transfer failed!')

In my earlier article the bugs were caused by external environment and tools/metrics like code coverage and mutation score are not affected by it. In fact the jinja-ab example falls into the category of data coverage testing.

The current example on the other hand is ignoring the return value of the withdraw() function and that's why it fails when we add the appropriate test.

NOTE: some mutation test tools support the removing/modifying return value mutation. Cosmic Ray doesn't support this at the moment (I should add it). Even if it did that would not help us find the bug because we would kill the mutation using the test_withdraw...() test methods, which already assert on the return value!

Thanks for reading and happy testing!

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Circo loco 2017

HackConf 2016

Due to popular demand I'm sharing my plans for the upcoming conference season. Here is a list of events I plan to visit and speak at (hopefully). The list will be updated throughout the year so please subscribe to the comments section to receive a notification when that happens! I'm open to meeting new people so ping me for a beer if you are attending some of these events!

02 February - Hack Belgium Pre-Event Workshops, Brussels

Note: added on Jan 12th

Last year I had an amazing time visiting an Elixir & Erlang workshop so I'm about to repeat the experience. I will be visiting a workshop organized by HackBelgium and keep you posted with the results.

03 February - Git Merge, Brussels

Note: added on Jan 12th

Git Merge is organized by GitHub and will be held in Brussels this year. I will be visiting only the conference track and hopefully giving a lightning talk titled Automatic upstream dependency testing with GitHub API! That and the afterparty of course!

04-05 February - FOSDEM, Brussels

FOSDEM is the largest free and open source gathering in Europe which I have been visiting since 2009 (IIRC). You can checkout some of my reports about FOSDEM 2014, Day 1, FOSDEM 2014, Day 2 and FOSDEM 2016.

I will present my Mutants, tests and zombies talk at the Testing & Automation devroom on Sunday.

UPDATE: Video recording is available here

I will be in Brussels between February 1st and 5th to explore the local start-up scene and get to meet with the Python community so ping me if you are around.

18 March - QA Challenge Accepted 3.0, Sofia

QA: Challenge Accepted is a specialized QA conference in Sofia and most of the sessions are in Bulgarian. I've visited last year and it was great. I even proposed a challenge of my own.

CFP is still open but I have a strong confidence that my talk Testing Red Hat Enterprise Linux the MicroSoft way will be approved. It will describe a large scale experiment with pairwise testing, which btw I learned about at QA: Challenge Accepted 2.0 :).

UPDATE: I will be also on the jury for QA of the year award.

UPDATE: I did a lightning talk about my test case management system (in Bulgarian).

07-08 April - Bulgaria Web Summit, Sofia

I have been a moderator at Bulgaria Web Summit for several years and this year is no exception. This is one of the strongest events held in Sofia and is in English. Last year over 60% of the attendees were from abroad so you are welcome!

I'm not going to speak at this event but will record as much of it as possible. UPDATE: Checkout the recordings on my YouTube channel!

10-12 May - Romanian Testing Conference, Cluj-Napoca

RTC'17 is a new event I found in neighboring Romania. The topic this year is Thriving and remaining relevant in Quality Assurance. My talk is titled Quality Assistance in the Brave New World where I'll share some experiences and visions for the QA profession if that gets accepted.

As it turned out I know a few people living in Cluj so I'll be arriving one day earlier on May 9th to meet the locals.

13-14 May - OSCAL, Tirana

Open Source Conference Albania is the largest OSS event in the country. I'm on a row here to explore the IT scene on the Balkans. Due to traveling constraints my availability will be limited to the conference venue only but I've booked a hotel across the street :).

I will be meeting a few friends in Tirana and hear about the progress of an psychological experiment we devised with Jona Azizaj and Suela Palushi.

Talking wise I'm hoping to get the chance of introducing mutation testing and even host a workshop on the topic.

UPDATE: Here is the video recording from OSCAL. The quality is very poor though.

20-21 May - DEVit, Thessaloniki

This is the 3rd edition of DEVit, the 360° web development conference of Northern Greece. I've been a regular visitor since the beginning and this year I've proposed a session on mutation testing. Because the Thessaloniki community seems more interested in Ruby and Rails my goal is to share more examples from my Ruby work and compare how that is different from the Python world. There is once again an opportunity for a workshop.

So far I've been the only Bulgarian to visit DEVit and also locally known as "The guy who Kosta & Kosta met in Sofia"! Checkout my impressions from DEVit'15 and DEVit'16 if you are still wondering whether to attend or not! I strongly recommend it!

UPDATE: I am still the only Bulgarian visiting DEVit!

22 May - Dev.bg, Sofia

I've hosted a session titled Quality Assurance According to Einstein for the local QA community in Sofia. Video (in Bulgarian) and links are available!

UPDATE: added post-mortem.

01-02 June - Shift Developer Conference, Split

Shift appears to be a very big event in Croatia. My attendance is still unconfirmed due to lots of traveling before that and the general trouble of efficiently traveling on the Balkans. However I have a CFP submitted and waiting for approval. This time it is my Mutation Testing in Patterns, which is a journal of different code patterns found during mutation testing. I have not yet presented it to the public but will blog about it sometime soon so stay tuned.

UPDATE: this one is a no-go!

03-04 June - TuxCon, Plovdiv

TuxCon is held in Plovdiv around the beginning of July. I'm usually presenting some lightning talks there and use the opportunity to meet with friends and peers outside Sofia and catch up with news from the local community. The conference is in Bulgarian with the exception of the occasional foreign speaker. If you understand Bulgarian I recommend the story of Puldin - a Bulgarian computer from the 80s.

UPDATE: I will be opening the conference with QA According to Einstein

17-18 June - How Camp, Varna

How Camp is the little brother of Bulgaria Web Summit and is always held outside of Sofia. This year it will be in Varna, Bulgaria. I will be there of course and depending on the crowd may talk about some software testing patterns.

UPDATE: it looks like this is also a no-go but stay tuned for the upcoming Macedonia Web Summit and Albania Web Summit where yours trully will probably be a moderator!

25-29 September - SuSE CON, Prague

Yeah, this is the conference organized by SuSE. I'm definitely not afraid to visit the competition. I even hope I could teach them something. More details are still TBA because this event is very close to/overlapping with the next two.

28-29 September - SEETEST, Sofia

South East European Software Testing Conference is, AFAIK, an international event which is hosted in a major city on the Balkans. Last year it was held in Bucharest with previous years held in Sofia.

In my view this is the most formal event, especially related to software testing, I'm about to visit. Nevertheless I like to hear about new ideas and some research in the field of QA so this is a good opportunity.

UPDATE: I have submitted a new talk titled If the facts don't fit the theory, change the facts!

30 September-1 October - HackConf, Sofia

HackConf is one of the largest conferences in Bulgaria, gathering over 1000 people each year. I am strongly affiliated with the people who organize it and even had the opportunity to host the opening session last year. The picture above is from this event.

The audience is still very young and inexperienced but the presenters are above average. Organizers' goal is HackConf to become the strongest technical conference in the country and also serve as a sort of inspiration for young IT professionals.

UPDATE: I have submitted both a talk proposal and a workshop proposal. For the workshop I intend to teach children Python and Selenium Automation in 8 hours. I've also been helping the organizers with bringing some very cool speakers from abroad!

October - IT Weekend, Bulgaria

IT Weekend is organized by Petar Sabev, the same person who's behind QA: Challenge Accepted. It is a non-formal gathering of engineers with the intent to share some news and then discuss and share problems and experiences. Checkout my review of IT Weekend #1 and IT Weekend #3.

The topic revolve around QA, leadership and management but the format is open and the intention is to broaden the topics covered. The event is held outside Sofia at a SPA hotel and makes for a very nice retreat. I don't have a topic but I'm definitely going if time allows. I will probably make something up if we have QA slots available :).

October - Software Freedom Kosova, Prishtina

Software Freedom Kosova is one of the oldest conferences about free and open source software in the region. This is part of my goal to explore the IT communities on the Balkans. Kosovo sounds a bit strange to visit but I did recognize a few names on the speaker list of previous years.

The CFP is not open yet but I'm planning to make a presentation. Also if weather allows I'm planning a road trip on my motorbike :).

UPDATE: I've met with some of the FLOSSK members in Tirana at OSCAL and they seem to be more busy with running the hacker space in Prishtina so the conference is nearly a no-go.

14-15 November - Google Test Automation Conference, London

GTAC 2017 will be held in London. Both speakers and attendees are pre-approved and my goal is to be the first Red Hatter and second Bulgarian to speak at GTAC.

The previous two years saw talks about mutation testing vs. coverage and their respective use to determine the quality of a test suite with both parties arguing against each other. Since I'm working in both of these fields and have at least two practical example I'm trying to gather more information and present my findings to the world.

UPDATE: I've also submitted my Testing Red Hat Enterprise Linux the Microsoft way

16-17 November - ISTA Con, Sofia

Innovations in Software Technologies and Automation started as a QA conference several years ago but it has broaden the range of acceptable topics to include development, devops and agile. I was at the first two editions and then didn't attend for a while until last year when I really liked it. The event is entirely in English with lots of foreign speakers.

Recently I've been working on something I call "Regression Test Monitoring" and my intention is to present this at ISTA 2017 so stay tuned.

UPDATE: I didn't manage to collect enough information on the Regression Test Monitoring topic but have made two other proposals.

Thanks for reading and see you around!

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QA & Automation 101 Retrospective

QA 101 graduation

At the beginning of this year I've hosted the first QA related course at HackBulgaria. This is a long overdue post about how the course went, what worked well and what didn't. Brace yourself because it is going to be a long one.

The idea behind a QA course has been lurking in both RadoRado's (from HackBulgaria) and my heads for quite a while. We've been discussing it at least a year before we actually started. One day Rado told me he'd found a sponsor and we have the go ahead for the course and that's how it all started!

The first issue was that we weren't prepared to start at a moments notice. I literally had two weeks to prepare the curriculum and initial interview questions. Next we opened the application form and left it open until the last possible moment. I've been reviewing candidate answers hours before the course started, which was another mistake we made!

On the positive side is that I hosted a Q&A session on YouTube answering general questions about the profession and the course itself. This live stream helped popularize the course.

At the start we had 30 people and around 13 of them managed to "graduate" till the final lesson. The biggest portion of students dropped out after the first 5 lessons of Java crash course! Each lesson was around 4 hours with 20-30 minutes break in the middle.

With respect to the criteria find a first job or find a new/better job I consider the training successful. To my knowledge all students have found better jobs, many of them as software testers!

On the practical side of things students managed to find and report 11 interesting bugs against Fedora. Mind you that these were all found in the wild: fedora-infrastructure #5323, RHBZ#1339701, RHBZ#1339709, RHBZ#1339713, RHBZ#1339719, RHBZ#1339731, RHBZ#1339739, RHBZ#1339742, RHBZ#1339746, RHBZ#1340541, RHBZ#1340891.

Then students also made a few pull requests on GitHub (3 which I know off): commons-math #38, commons-csv #12, commons-email #1.

Lesson format

For reference most lessons were a mix of short presentation about theory and best practices followed by discussions and where appropriate practical sessions with technology or projects. The exercises were designed for individual work, work in pairs or small groups (4-5) on purpose.

By request from the sponsors I've tried to keep a detailed record of each student's performance and personality traits as much as I was able to observe them. I really enjoyed keeping such a journal but didn't share this info with my students which I consider a negative issue. I think knowing where your strong and weak areas are would help you become a better expert in your field!

Feedback from students

  • There was little time (to work on the practical examples I guess);
  • Not having particular practical tasks was a problem. For example we didn't have tasks of the sort do "X" then "Y";
  • They needed more time and more attention to be given to them;
  • Installing different pieces of software and tools took a lot of time and frustration. It was also quite problematic sometimes depending on whether they used Linux, Windows or Mac OS X;
  • Working with Eclipse IDE was horrible. Nobody new what to do and the interface wasn't newbie friendly. Also it took quite a lot of time to install dependencies and/or import projects to run in Eclipse;
  • There were a few problems with Selenium and its different versions being used.

I have to point out that while these are valid concerns and major issues students were at least partially guilty for the last 3 of them. It was my impression that most of them didn't prepare at home, didn't read the next lesson and didn't install prerequisite tools and software!

5x Java Crash Course

We've started with a Java crash course as requested by our sponsors which was extended to 5 instead of the original 3 sessions. RadoRado was teaching Java fundamentals while I was assisting him with comments.

On the good side is that Rado explains very well and in much details. He also writes code to demonstrate what he teaches and while doing so uses only the knowledge he's presented so far. For example if there's a repeating logic/functionality he would just write it twice instead of refactoring that into a separate function with parameters (assuming the students have not learned about functions yet). I think this made it more easier to understand the concepts being taught.

Another positive thing we did was me going behind Rado's computer and modifying some of the code while he was explaining something on screen. If you take the above example and have two methods with print out salutations, e.g. "Good morning, Alex" I would go and modify one of them to include "Mr." while the other will not. This introduced a change in behavior which ultimately results in a bug! This was a nice practical way to demonstrate how some classes of bugs get introduced in reality. We did only a few of these behind the computer changes and I definitely liked them! They were all ad-hoc, not planned for.

On the negative side Java seems hard to learn and after these 5 lessons half of the students dropped out. Maybe part of the reason is they didn't expect to start a QA course with lessons about programming. But that also means they didn't pay enough attention to the curriculum, which was announced in advance!

Lesson 01 - QA Fundamentals

I had made a point to assign time constraints to each exercise in the lessons. While that mostly worked in the first few lessons, where there is more theory, we didn't keep the schedule and were overtime.

Explaining testing theory (based on ISTQB fundamentals) took longer than I expected. it was also evident that we needed more written examples of what different test analysis techniques are (e.g. boundary value analysis). Here Petar Sabev helped me deliver few very nice examples.

One of the exercises was "when to stop testing" with an example of a Sudoku solving function and different environments in which this code operates, e.g. browser, mobile, etc. Students appeared to have a hard time understanding what a "runtime environment" is and define relevant tests based on that! I believe most of the students, due to lack of knowledge and experience, were also having a hard time grasping the concept of non-functional testing.

A positive thing was that students started explaining to one another and giving examples for bugs they've seen outside the course.

Lesson 02 - Software Development Lifecycle

This lesson was designed as role playing game to demonstrate the most common software development methodologies - waterfall and agile and discuss the QA role in both of them. The format by itself is very hard to conduct successfully and this was my first time ever doing this. I've also never taken part of such games until then, only heard about them.

During the waterfall exercise it was harder for the students to follow the game constraints and not exchange information with one another because they were sitting on the same table.

On the positive side all groups came with unique ideas about software features and how they want to develop them. Timewise we managed to do very well. On the negative side is that I was the client for all groups and didn't manage to pay enough attention to everyone, which btw is what clients usually do in real life.

Lesson 03 - Bug Tracking

This lesson was a practical exercise in writing bug reports and figuring out what information needs to be present in a good bug report. Btw this is something I always ask junior members at job interviews.

First we started with working in pairs to define what a good bug report is without actually knowing what that means. Students found it hard to brainstorm together and most of them worked alone during this exercise.

Next students had to write bug reports for some example bugs, which I've explained briefly on purpose and perform peer reviews of their bugs. Reviews took a long time to complete but overall students had a good idea of what information to include in a bug report.

Then, after learning from their mistakes and hearing what others had done, they've learned about some good practices and were tasked to rewrite their bug reports using the new knowledge. I really like the approach of letting students make some mistakes and then showing them the easier/better way of doing things. This is also on-par with Ivan Nemytchenko's methodology of letting his interns learn by their mistakes.

All bug reports can be found in students repositories, which are forked from the curriculum. Check out https://github.com/HackBulgaria/QA-and-Automation-101/network.

I should have really asked everyone to file bugs under the curriculum repository so it is easier for me to track them. On the other hand I wanted each student to start building their own public profile to show potential employers.

Lesson 04 - Test Case Management

This lesson started with an exercise asking students to create accounts for Red Hat's OpenShift cloud platform in the form of a test scenario. The scenario intentionally left out some details. The idea being that missing information introduces inconsistencies during testing and to demonstrate how the same steps were performed slightly differently.

We had some troubles explaining exactly "how did you test" because most inexperienced people would not remember all details about where they clicked, did they use the mouse or the keyboard, was the tab order correct, etc. Regardless students managed to receive different results and discover that some email providers were not supported.

The homework assignment was to create test plans and test cases in Nitrate at https://nitrate-hackbg.rhcloud.com/. Unfortunately the system appears to be down ATM and I don't have time to investigate why. This piece of infrastructure was put together in 2 hours and I'm surprised it lasted without issues during the entire course.

2x Introduction to Linux

This was a crash course in Linux fundamentals and exercise with most common commands and text editors in the console. Most of the students were not prepared with virtual machines. We've also used a cloud provider to give students remote shell but the provider API was failing and we had to deploy docker containers manually. Overall infrastructure was a big problem but we somehow managed. Another problem was with ssh clients from Windows who generated keys in a format that our cloud provider couldn't understand.

Wrt commands and exercises students did well and managed to execute most of them on their own. That's very good for people who've never seen a terminal in their lives (more or less).

Lesson 05 - Testing Fedora 24(25) Changes

Once again nobody was prepared with a virtual machine with Fedora and students were installing software as we go. Because of that we didn't manage to conduct the lesson properly and had to repeat it on the next session.

Rawhide being the bleeding edge of Fedora means it is full of bugs. Well I couldn't keep up with everyone and explain workarounds or how to install/upgrade Fedora. That was a major setback. It also became evident that you can't move quickly if you have no idea what to do and no instructions about it either.

Lesson 05 - Again

Once prepared with the latest and greatest from Rawhide the task was to analyze the proposed feature changes (on the Fedora wiki) and create test plans and design test cases for said changes. Then execute the tests in search for bugs. This is where some of the bugs above came from. The rest were found during upgrades.

This lesson was team work (4-5 students) but the results were mixed. IMO Fedora changes are quite hard to grasp, especially if you lack domain knowledge and broader knowledge about the structure and operation of a Linux distribution. I don't think most teams were able to clearly understand their chosen features and successfully create good plans/scenarios for them. On the other hand in real life software you don't necessarily understand the domain better and know what to do. I've been in situations where whole features have been defined by a single sentence and requested to be tested by QA.

One of the teams didn't manage to install Fedora (IIRC they didn't have laptops capable of running a VM) and were not able to conduct the exercise.

Being able to find real life bugs, some of them serious, and getting traction in Bugzilla is the most positive effect of this lesson. I personally wanted to have more output (e.g. more bugs, more cases defined, etc) but taking into account the blocking factors and setbacks I think this is a good initial result.

Lesson 06 - Unit Testing and Continuous Integration

Here we had a few examples of bad stubs and mocks which were not received very well. The topic is hard in itself and wasn't very well explained with practical examples.

Another negative thing is that students took a lot of time to fiddle around with Eclipse, they were mistyping commands in the terminal and generally not paying enough attention to instructions. This caused the exercises to go slowly.

We've had an exercise which asks the student to write a new test for a non-existing method. Then implement the method and make sure all the tests passed. You guessed it this is Test Driven Development. IIRC one of the students was having a hard time with that exercise so I popped up my editor on the large screen and started typing what she told me, then re-running the tests and asking her to show me the errors I've made and tell me how to correct them. The exercise was received very well and was fun to do.

Due to lack of time we had to go over TravisCI very quickly. The other bad thing about TravisCI is that it requires git/GitHub and the students were generally inexperienced with that. Both GitHub for Windows and Mac OS suck a big time IMO. What you need is the console. However none of the students had any practical experience with git and knew how to commit code and push branches to GitHub. git fundamentals however is a separate one or two lessons by itself which we didn't do.

Lesson 07 - Writing JUnit tests for Apache Commons

Excluding the problems with Eclipse and the GitHub desktop client and missing instructions for Windows the hardest part of this lesson was actually selecting a component to work on, understanding what the code does and actually writing meaningful tests. On top of that most students were not very proficient programmers and Java was completely new to them.

Despite having 3 pull requests on GitHub I consider this lesson to be a failure.

Lesson 08 - Integration Testing with Selenium

This lesson starts with an example of what a flaky test it. At the moment I don't think this lesson is the best place for that example. To make things even more difficult the example is in Python (because that way was the easiest for me to write it) instead of Java. Students had problems installing Python on Windows just to make this example work. They also were lacking the knowledge how to execute a script in the terminal.

One of the students proposed a better flaky example utilizing dates and times and executing it during various hours of the day. I have yet to code this and prepare environment in which it would be executed. Btw recently I've seen similar behavior caused by inconsistent timezone usage in Ruby which resulted in unexpected time offset a little after midnight :).

Once again I have to point out that students came generally unprepared for the lesson and haven't installed prerequisite software and programming languages. This is becoming a trend and needs to be split out into a preparation session, possibly with a check list.

On the Selenium side, starting with Selenium IDE, it was a bit unclear how to use it and what needs to be done. This is another negative trend, where students were missing clear instructions what they are expected to do. At the end we did resort to live demo using Selenium IDE so they can at least get some idea about it.

Lesson 09 and 10 - Writing Selenium tests for Mozilla Add-ons website

IMO these two lessons are the biggest disaster of the entire course. Python & virtualenv on Windows was a total no go but on Linux things weren't much easier because students had no idea what a virtualenv is.

Practice wise they haven't managed to read all the bugs on the Mozilla bug tracker and had a very hard time selecting bugs to write tests for. Not to mention that many of the reported bugs were administrative tasks to create or remove add-on categories. There weren't many functional related bugs to write tests for.

The product under test was also hard to understand and most students were seeing it for the first time, let alone getting to know the devel and testing environments that Mozilla provides. Mozilla's test suite being in Python is just another issue to make contribution harder because we've never actually studied Python.

Between the two lessons there were students who've missed the Selenium introduction lesson and were having even harder time to figure things out. I didn't have the time to explain and go back to the previous lesson for them. Maybe an attendance policy is needed for dependent lessons.

Before the course started I've talked to some guys at Mozilla's IRC channel and they agreed to help but at the end we didn't even engage with them. At this point I'm skeptical that mentoring over IRC would have worked anyway.

Lesson 11 - Introduction to Performance Testing

This was a more theoretical lesson with less practical examples and exercises. I have provided some blog posts of mine related to the topic of performance testing but in general they are related to software that I've used which isn't generally known to a less experienced audience (Celery, Twisted). These blog posts IMO were hard to put into perspective and didn't serve a good purpose as examples.

The practical part of the lesson was a discussion with the goal of creating a performance testing strategy for GitHub's infrastructure. It was me who was doing most of the talking because students have no experience working on such a large infrastructure like GitHub and didn't know what components might be there, how they might be organized (load balancers, fail overs, etc) and what needs to be tested.

There was also a more practical example to create a performance test in Java for one of the classes found in commons-codec/src/main/java/org/apache/commons/codec/digest. Again the main difficulty here was working fluently with Eclipse, getting the projects to build/run and knowing how the software under test was supposed to work and be executed.

Lesson 12 - How to find 1000 bugs in 30 minutes

This was a more relaxed lesson with examples of simple types of bugs found on a large scale. Most examples came from my blog and experiments I've made against Fedora.

While amusing and fun I don't think all of the students understood me and kept their attention. Part of that is because Fedora tends to focus on low level stuff and my examples were not necessarily easy to understand.

Feedback from the sponsor

Experian Bulgaria was the exclusive sponsor for this course. At the end of the summer Rado and I met with them to discuss the results of the training. Here's what they say

  • Overall technical knowledge they consider to be weak. What they need are people with basic knowledge in the field of object oriented programming, databases, operating systems and networking. These are skills candidates need in order to work for Experian. It must be noted that most of them were not taught at this course!
  • English language proficiency for all students is low on average;
  • User level experience with Linux was fine but students were missing deeper knowledge about the operating system. Once again something we didn't teach;
  • The programming languages favored at Experian are Java and Ruby and students had poor knowledge of them. They also had weak understanding of OOP principles;
  • According to Experian students were more ingrained with the development mindset and were trying their luck in the QA profession instead of genuinely being interested in the field. While this is generally the case I have to point out that as sponsor Experian did a poor job at promoting their company and the QA profession as a whole. What isn't known to the general public is their big in-house QA community which could have served as a source of inspiration for the students!
  • Low motivation and lack of fundamental knowledge from university are other traits interviewers at Experian have identified. They argued for a stronger acceptance process and a requirement of minimum 2 years of university education in computer science.

On the topic of testing knowledge candidates did mostly OK, however we don't have enough information about this. Also the hiring process at Experian is more focused on the broader knowledge areas listed above so substantial improvement in the testing knowledge of candidates doesn't given them much head start.

While to my knowledge they didn't hire anyone few people received an offer but declined due to various personal reasons. I view this as poor performance on our side but Experian thinks otherwise and are willing to sponsor another round of training.


Here is a list of all the things that could be improved

  • Take time to develop the curriculum and have it pass QA review by other experienced testers (in particular such that also teach students);
  • Make the application process harder to include people with broader IT knowledge;
  • Allow time to review all applicants;
  • Find a co-trainer and additional mentors for some of the exercises;
  • Minimize the number of students accepted in the course so we can handle everyone with more care;
  • Give homework assignments and examine them before each lesson;
  • Collect and provide performance review at the end of the course;
  • Minimize the technology stack and tools used;
  • Host a technology preparation session at the beginning paired with a check list of all the things that need to be done. Very likely make the chosen technology stack a hard requirement to avoid setbacks later in the schedule;
  • We need more fundamental lessons like practical git tutorial, practical Linux tutorial, databases, networking, etc.
  • Same goes for Java or any other programming language. Each of these technologies easily makes a course by itself. Possibly include technology skill assessment in the application form and reject candidates who don't meet the minimum level. This is to ensure the group is able to move at the same pace.
  • We need to improve the infrastructure used during the course, especially exercise bug tracking and test case management systems;
  • Students need clear instructions for every exercise - what is required from them, what the expected result is and what they need to be doing, etc;
  • Provide more examples for just about everything. Also make the examples easier to understand/simple with the harder examples left for further reading;
  • Provide easier projects to work on. This means applications whose domain is easier to understand and closer to what experiences the students might have. Also projects need clear instructions how to join and how to contribute with tests.
  • The same application/software needs to be used for manual bug finding, unit test writing and integration test with Selenium. This will minimize both context and technology switches and allow to view various testing activities in the context of a single software under test;
  • While using open source projects for the above listed purposes sounds great the reality is that they are hard to join and will not move according to our schedule. Maybe less focus on open source per-se and more focus on a particular application under test. Instructors can then proxy all the tests forward to the upstream community;
  • Focus more on practice and less on exotic topics like performance testing and large scale bug finding;
  • Seek more active participation from sponsors!

If you have suggestions please comment below, especially if you can tell me how to implement them in practice.

Thanks for reading and happy testing!

There are comments.

4 Quick Wins to Manage the Cost of Software Testing

Every activity in software development has a cost and a value. Getting cost to
trend down while increasing value, is the ultimate goal.

This is the introduction of an e-book called 4 Quick Wins to Manage the Cost of Software Testing. It was sent to me by Ivan Fingarov couple of months ago. Just now I've managed to read it and here's a quick summary. I urge everyone to download the original copy and give it a read.

The paper focuses on several practices which organizations can apply immediately in order to become more efficient and transparent in their software testing. While larger organizations (e.g. enterprises) have most of these practices already in place smaller companies (up to 50-100 engineering staff) may not be familiar with them and will reap the most benefits of implementing said practices. Even though I work for a large enterprise I find this guide useful when considered at the individual team level!

The first chapter focuses on Tactics to minimize cost: Process, Tools, Bug System Mining and Eliminating Handoffs.

In Process the goal is to minimize the burden of documenting the test process (aka testing artifacts), allow for better transparency and visibility outside the QA group and streamline the decision making process of what to test and when to stop testing, how much has been tested, what the risk is, ect. The authors propose testing core functionality paired with emerging risk areas based on new features development. They propose making a list of these and sorting that list by perceived risk/priority and testing as much as possible. Indeed this is very similar to the method I've used at Red Hat when designing testing for new features and new major releases of Red Hat Enterprise Linux. A similar method I've seen in place at several start-ups as well, although in the small organization the primary driver for this method is lack of sufficient test resources.

Tools proposes the use of test case management systems to ease the documentation burden. I've used TestLink and Nitrate. From them Nitrate has more features but is currently unmaintained with me being the largest contributor on GitHub. From the paid variants I've used Polarion which I generally dislike. Polarion is most suitable for large organizations because it gives lots of opportunities for tracking and reporting. For small organizations it is an overkill.

Bug System Mining is a technique which involves regularly scanning the bug tracker and searching for patterns. This is useful for finding bug types which appear frequently and generally point to a flaw in the software development process. The fix for these flaws usually is a change in policy/workflow which eliminates the source of the errors. I'm a fan of this technique when joining an existing project and need to assess what the current state is. I've done this when consulting for a few start-ups, including Jitsi Meet (acquired by Atlassian), however I'm not doing bug mining on a regular basis which I consider a drawback and I really should start doing!

For example at one project I found lots of bugs reported against translations, e.g. missing translations, text overflowing the visible screen area or not playing well with existing design, chosen language/style not fitting well with the product domain, etc.

The root cause of the problem was how the software in question has been localized. The translators were given a file of English strings, which they would translate and return back in an spread sheet. Developers would copy&paste the translated strings into localization files and integrate with the software. Then QA would usually inspect all the pages and report the above issues. The solution was to remove devel and QA from the translation process, implement a translation management system together with live preview (web based) so that translators can keep track of what is left to translate and can visually inspect their work immediately after a string was translated. Thus translators are given more context for their work but also given the responsibility to produce good quality translations.

Another example I've seen are many bugs which seem like a follow up/nice to have features of partially implemented functionality. The root cause of this problem turned out to be that devel was jumping straight to implementation without taking the time to brainstorm and consult with QE and product owners, not taking into account corner cases and minor issues which would have easily been raised by skillful testers. This process lead to several iterations until the said functionality was considered initially implemented.

Eliminating Handoffs proposes the use of cross-functional teams to reduce idle time and reduce the back-and-forth communication which happens when a bug is found, reported, evaluated and considered for a fix, fixed by devel and finally deployed for testing. This method argues that including testers early in the process and pairing them with the devel team will produce faster bug fixes and reduce communication burden.

While I generally agree with that statement it's worth noting that cross-functional teams perform really well when all team members have relatively equal skill level on the horizontal scale and strong experience on the vertical scale (think T-shaped specialist). Cross-functional teams don't work well when you have developers who aren't well versed in the testing domain and/or testers who are not well versed in programming or the broader OS/computer science fundamentals domain. In my opinion you need well experienced engineers for a good cross-functional team.

In the chapter Collaboration the paper focuses on pairing, building the right thing and faster feedback loops for developers. This overlaps with earlier proposals for cross-functional teams and QA bringing value by asking the "what if" questions. The chapter specifically talks about the Three Amigos meeting between PM, devel and QA where they discuss a feature proposal from all angles and finally come to a conclusion what the feature should look like. I'm a strong supporter of this technique and have been working with it under one form or another during my entire career. This also touches on the notion that testers need to move into the Quality Assistance business and be proactive during the software development process, which is something I'm hoping to talk about at the Romanian Testing Conference next year!

Finally the book talks about Skills Development and makes the distinction between Centers of Excellence (CoE) and Communities of Practice (CoP). Both the book and I are supporters of the CoP approach. This is a bottoms-up approach which is open for everyone to join in and harnesses the team creative abilities. It also takes into account that different teams use different methods and tools and that "one size doesn't fit all"!

Skilled teams find important bugs faster, discover innovative solutions to hard
testing problems and know how to communicate their value. Sometimes, a few super
testers can replace an army of average testers.

While I consider myself to be a "super tester" with thousands of bugs reported there is a very important note to make here. Communities of Practice are successful when their members are self-focused on skill development! In my view and to some extent the communities I've worked with everyone should strive to constantly improve their skills but also exercise peer pressure on their co-workers to not fall behind. This has been confirmed by other folks in the QA industry and I've heard it many times when talking to friends from other companies.

Thanks for reading and happy testing!

There are comments.

Mutation Testing vs. Coverage

At GTAC 2015 Laura Inozemtseva made a lightning talk titled Coverage is Not Strongly Correlated with Test Suite Effectiveness which is the single event that got me hooked up with mutation testing. This year, at GTAC 2016, Rahul Gopinath made a counter argument with his lightning talk Code Coverage is a Strong Predictor of Test Suite Effectiveness. So which one is better ? I urge you to watch both talks and take notes before reading about my practical experiment and other opinions on the topic!

DISCLAIMER: I'm a heavy contributor to Cosmic-Ray, the mutation testing tool for Python so my view is biased!

Both Laura and Rahul (you will too) agree that a test suite effectiveness depends on the strength of its oracles. In other words the assertions you make in your tests. This is what makes a test suite good and determines its ability to detect bugs when present. I've decided to use pelican-ab as a practical example. pelican-ab is a plugin for Pelican, the static site generator for Python. It allows you to generate A/B experiments by writing out the content into different directories and adjusting URL paths based on the experiment name.

Can 100% code coverage detect bugs

Absolutely NOT! In version 0.2.1, commit ef1e211, pelican-ab had the following bug:

Given: Pelican's DELETE_OUTPUT_DIRECTORY is set to True (which it is by default)
When: we generate several experiments using the commands:
    AB_EXPERIMENT="control" make regenerate
    AB_EXPERIMENT="123" make regenerate
    AB_EXPERIMENT="xy" make regenerate
    make publish
Actual result: only the "xy" experiment (the last one) would be published online.
And: all of the other contents will be deleted.

Expected result: content from all experiments will be available under the output directory.

This is because before each invocation Pelican deletes the output directory and re-creates the entire content structure. The bug was not caught regardless of having 100% line + branch coverage. See Build #10 for more info.

Can 100% mutation coverage detect bugs

So I've branched off since commit ef1e211 into the mutation_testing_vs_coverage_experiment branch (requires Pelican==3.6.3).

After initial execution of Cosmic Ray I have 2 mutants left:

$ cosmic-ray run --baseline=10 --test-runner=unittest example.json pelican_ab -- tests/
$ cosmic-ray report example.json 
job ID 29:Outcome.SURVIVED:pelican_ab
command: cosmic-ray worker pelican_ab mutate_comparison_operator 3 unittest -- tests/
--- mutation diff ---
--- a/home/senko/pelican-ab/pelican_ab/__init__.py
+++ b/home/senko/pelican-ab/pelican_ab/__init__.py
@@ -14,7 +14,7 @@
     def __init__(self, output_path, settings=None):
         super(self.__class__, self).__init__(output_path, settings)
         experiment = os.environ.get(jinja_ab._ENV, jinja_ab._ENV_DEFAULT)
-        if (experiment != jinja_ab._ENV_DEFAULT):
+        if (experiment > jinja_ab._ENV_DEFAULT):
             self.output_path = os.path.join(self.output_path, experiment)
             Content.url = property((lambda s: ((experiment + '/') + _orig_content_url.fget(s))))
             URLWrapper.url = property((lambda s: ((experiment + '/') + _orig_urlwrapper_url.fget(s))))

job ID 33:Outcome.SURVIVED:pelican_ab
command: cosmic-ray worker pelican_ab mutate_comparison_operator 7 unittest -- tests/
--- mutation diff ---
--- a/home/senko/pelican-ab/pelican_ab/__init__.py
+++ b/home/senko/pelican-ab/pelican_ab/__init__.py
@@ -14,7 +14,7 @@
     def __init__(self, output_path, settings=None):
         super(self.__class__, self).__init__(output_path, settings)
         experiment = os.environ.get(jinja_ab._ENV, jinja_ab._ENV_DEFAULT)
-        if (experiment != jinja_ab._ENV_DEFAULT):
+        if (experiment not in jinja_ab._ENV_DEFAULT):
             self.output_path = os.path.join(self.output_path, experiment)
             Content.url = property((lambda s: ((experiment + '/') + _orig_content_url.fget(s))))
             URLWrapper.url = property((lambda s: ((experiment + '/') + _orig_urlwrapper_url.fget(s))))

total jobs: 33
complete: 33 (100.00%)
survival rate: 6.06%

The last one, job 33 is equivalent mutation. The first one, job 29 is killed by the test added in commit b8bff85. For all practical purposes we now have 100% code coverage and 100% mutation coverage. The bug described above still exists thought.

How can we detect the bug

The bug isn't detected by any test because we don't have tests designed to perform and validate the exact same steps that a physical person will execute when using pelican-ab. Such test is added in commit ca85bd0 and you can see that it causes Build #22 to fail.

Experiment with setting DELETE_OUTPUT_DIRECTORY=False in tests/pelicanconf.py and the test will PASS!

Is pelican-ab bug free

Not of course. Even after 100% code and mutation coverage and after manually constructing a test which mimics user behavior there is at least one more bug present. There is a pylint bad-super-call error, fixed in commit 193e3db. For more information about the error see this blog post.

Other bugs found

During my humble experience with mutation testing so far I've added quite a few new tests and discovered two bugs which went unnoticed for years. The first one is constructor parameter not passed to parent constructor, see PR#96, pykickstart/commands/authconfig.py

     def __init__(self, writePriority=0, *args, **kwargs):
-        KickstartCommand.__init__(self, *args, **kwargs)
+        KickstartCommand.__init__(self, writePriority, *args, **kwargs)
         self.authconfig = kwargs.get("authconfig", "")

The second bug is parameter being passed to parent class constructor, but the parent class doesn't care about this parameter. For example PR#96, pykickstart/commands/driverdisk.py

-    def __init__(self, writePriority=0, *args, **kwargs):
-        BaseData.__init__(self, writePriority, *args, **kwargs)
+    def __init__(self, *args, **kwargs):
+        BaseData.__init__(self, *args, **kwargs)

Also note that pykickstart has nearly 100% test coverage as a whole and the affected files were 100% covered as well.

The bugs above don't seem like a big deal and when considered out of context are relatively minor. However pykickstart's biggest client is anaconda, the Fedora and Red Hat Enterprise Linux installation program. Anaconda uses pykickstart to parse and generate text files (called kickstart files) which contain information for driving the installation in a fully automated manner. This is used by everyone who installs Linux on a large scale and is pretty important functionality!

writePriority controls the order of which individual commands are written to file at the end of the installation. In rare cases the order of commands may depend on each other. Now imagine the bugs above produce a disordered kickstart file, which a system administrator thinks should work but it doesn't. It may be the case this administrator is trying to provision hundreds of Linux systems to bootstrap a new data center or maybe performing disaster recovery. You get the scale of the problem now, don't you?

To be honest I've seen bugs of this nature but not in the last several years.

This is all to say a minor change like this may have an unexpectedly big impact somewhere down the line.


With respect to the above findings and my bias I'll say the following:

  • Neither 100% coverage, nor 100% mutation coverage are a silver bullet against bugs;
  • 100% mutation coverage appears to be better than 100% code coverage in practice;
  • Mutation testing clearly shows out pieces of code which need refactoring which in turn minimizes the number of possible mutations;
  • Mutation testing causes you to write more asserts and construct more detailed tests which is always a good thing when testing software;
  • You can't replace humans designing test cases just yet but can give them tools to allow them to write more and better tests;
  • You should not rely on a single tool (or two of them) because tools are only able to find bugs they were designed for!

Bonus: What others think

As a bonus to this article let me share a transcript from the mutation-testing.slack.com community:

atodorov 2:28 PM
Hello everyone, I'd like to kick-off a discussion / interested in what you think about
Rahul Gopinath's talk at GTAC this year. What he argues is that test coverage is still
the best metric for how good a test suite is and that mutation coverage doesn't add much
additional value. His talk is basically the opposite of what @lminozem presented last year
at GTAC. Obviously the community here and especially tools authors will have an opinion on
these two presentations.

tjchambers 12:37 AM
@atodorov I have had the "pleasure" of working on a couple projects lately that illustrate
why LOC test coverage is a misnomer. I am a **strong** proponent of mutation testing so will
declare my bias.

The projects I have worked on have had a mix of test coverage - one about 50% and
another > 90%.

In both cases however there was a significant difference IMO relative to mutation coverage
(which I have more faith in as representative of true tested code).

Critical factors I see when I look at the difference:

- Line length: in both projects the line lengths FAR exceeded visible line lengths that are
"acceptable". Many LONGER lines had inline conditionals at the end, or had ternary operators
and therefore were in fact only 50% or not at all covered, but were "traversed"

- Code Conviction (my term): Most of the code in these projects (Rails applications) had
significant Hash references all of which were declared in "traditional" format hhh[:symbol].
So it was nearly impossible for the code in execution to confirm the expectation of the
existence of a hash entry as would be the case with stronger code such as "hhh.fetch(:symbol)"

- Instance variables abound: As with most of Rails code the number of instance variables
in a controller are extreme. This pattern of reference leaked into all other code as well,
making it nearly impossible with the complex code flow to ascertain proper reference
patterns that ensured the use of the instance variables, so there were numerous cases
of instance variable typos that went unnoticed for years. (edited)

- .save and .update: yes again a Rails issue, but use of these "weak" operations showed again
that although they were traversed, in many cases those method references could be removed
during mutation and the tests would still pass - a clear indication that save or update was
silently failing.

I could go on and on, but the mere traversal of a line of code in Ruby is far from an indication
of anything more than it may be "typed in correctly".

@atodorov Hope that helps.

LOC test coverage is a place to begin - NOT a place to end.

atodorov 1:01 AM
@tjchambers: thanks for your answer. It's too late for me here to read it carefully but
I'll do it tomorrow and ping you back

dkubb 1:13 AM
As a practice mutation testing is less widely used. The tooling is still maturing. Depending on your
language and environment you might have widely different experiences with mutation testing

I have not watched the video, but it is conceivable that someone could try out mutation testing tools
for their language and conclude it doesn’t add very much

mbj 1:14 AM
Yeah, I recall talking with @lminozem here and we identified that the tools she used likely
show high rates of false positives / false coverage (as the tools likely do not protect against
certain types of integration errors)

dkubb 1:15 AM
IME, having done TDD for about 15+ years or so, and mutation testing for about 6 years, I think
when it is done well it can be far superior to using line coverage as a measurement of test quality

mbj 1:16 AM
Any talk pro/against mutation testing must, as the tool basis is not very homogeneous, show a non consistent result.

dkubb 1:16 AM
Like @tjchambers says though, if you have really poor line coverage you’re not going to
get as much of a benefit from mutation testing, since it’s going to be telling you what
you already know — that your project is poorly tested and lots of code is never exercised

mbj 1:19 AM
Thats a good and likely the core point. I consider that mutation testing only makes sense
when aiming for 100% (and this is to my experience not impractical).

tjchambers 1:20 AM
I don't discount the fact that tool quality in any endeavor can bring pro/con judgements
based on particular outcomes

dkubb 1:20 AM
What is really interesting for people is to get to 100% line coverage, and then try mutation
testing. You think you’ve done a good job, but I guarantee mutation testing will find dozens
if not hundreds of untested cases .. even in something with 100% line coverage

To properly evaluate mutation testing, I think this process is required, because you can’t
truly understand how little line coverage gives you in comparison

tjchambers 1:22 AM
But I don't need a tool to tell me that a 250 character line of conditional code that by
itself would be an oversized method AND counts more because there are fewer lines in the
overall percentage contributes to a very foggy sense of coverage.

dkubb 1:22 AM
It would not be unusual for something with 100% line coverage to undergo mutation testing
and actually find out that the tests only kill 60-70% of possible mutations

tjchambers 1:22 AM
@dkubb or less

dkubb 1:23 AM
usually much less :stuck_out_tongue:

it can be really humbling

mbj 1:23 AM
In this discussion you miss that many test suites (unless you have noop detection):
Will show false coverage.

tjchambers 1:23 AM
When I started with mutant on my own project which I developed I had 95% LOC coverage

mbj 1:23 AM
Test suites need to be fixed to comply to mutation testing invariants.

tjchambers 1:23 AM
I had 34% mutation coverage

And that was ignoring the 5% that wasn't covered at all

mbj 1:24 AM
Also if the tool you compare MT with line coverage on: Is not very strong,
the improvement may not be visible.

dkubb 1:24 AM
another nice benefit is that you will become much better at enumerating all
the things you need to do when writing tests

tjchambers 1:24 AM
@dkubb or better yet - when writing code.

The way I look at it - the fewer the alive mutations the better the test,
the fewer the mutations the better the code.

dkubb 1:29 AM
yeah, you can infer a kind of cyclomatic complexity by looking at how many mutations there are

tjchambers 1:31 AM
Even without tests (not recommended) you can judge a lot from the mutations themselves.

I still am an advocate for mutations/LOC metric

As you can see members in the community are strong supporters of mutation testing, all of them having much more experience than I do.

Please help me collect more practical examples! My goal is to collect enough information and present the findings at GTAC 2017 which will be held in London.

UPDATE: I have written Mutation testing vs. coverage, Pt.2 with another example.

Thanks for reading and happy testing!

There are comments.

How to create auxiliary build jobs in Travis-CI matrix

Auxiliary build job in Travis-CI

In Travis-CI when you combine the three main configuration options of Runtime (language), Environment and Exclusions/Inclusions you get a build matrix of all possible combinations! For example, for django-chartit the matrix includes 43 build jobs, spread across various Python and Django versions. For reference see Build #75.

For django-chartit I wanted to have an additional build job which would execute pylint. I wanted the job to be independent because currently pylint produces lots of errors and warnings. Having an independent job instead of integrating pylint together with all jobs makes it easier to see if any of the functional tests failed.

Using the inclusion functionality of Travis-CI I was able to define an auxiliary build job. The trick is to provide sane environment defaults for all build jobs (regular and auxiliary ones) so you don't have to expand your environment section! In this case the change looks like this

diff --git a/.travis.yml b/.travis.yml
index 67f656d..9b669f9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,8 @@ after_success:
 - coveralls
 - pip install coveralls
+- if [ -z "$_COMMAND" ]; then export _COMMAND=coverage; fi
+- if [ -z "$_DJANGO" ]; then export _DJANGO=1.10.4; fi
 - !!python/unicode '_DJANGO=1.10'
 - !!python/unicode '_DJANGO=1.10.2'
@@ -41,6 +43,10 @@ matrix:
     python: 3.3
   - env: _DJANGO=1.10.4
     python: 3.3
+  include:
+  - env: _COMMAND=pylint
+    python: 3.5
     on_failure: change
@@ -50,4 +56,4 @@ python:
 - 3.3
 - 3.4
 - 3.5
-script: make coverage
+script: make $_COMMAND

For more info take a look at commit b22eda7 and Build #77. Note Job #77.44!

Thanks for reading and happy testing!

There are comments.

Overridden let() causes segfault with RSpec

Last week Anton asked me to take a look at one of his RSpec test suites. He was able to consistently reproduce a segfault which looked like this:

/home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:113: [BUG] vm_call_cfunc - cfp consistency error
ruby 2.3.2p217 (2016-11-15 revision 56796) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0013 p:---- s:0048 e:000047 CFUNC  :map
c:0012 p:0011 s:0045 e:000044 BLOCK  /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:113
c:0011 p:0035 s:0043 e:000042 METHOD /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration.rb:1835
c:0010 p:0011 s:0040 e:000039 BLOCK  /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:112
c:0009 p:0018 s:0037 e:000036 METHOD /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/reporter.rb:77
c:0008 p:0022 s:0033 e:000032 METHOD /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:111
c:0007 p:0025 s:0028 e:000027 METHOD /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:87
c:0006 p:0085 s:0023 e:000022 METHOD /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:71
c:0005 p:0026 s:0016 e:000015 METHOD /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:45
c:0004 p:0025 s:0012 e:000011 TOP    /home/atodorov/.rbenv/versions/2.3.2/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/exe/rspec:4 [FINISH]
c:0003 p:---- s:0010 e:000009 CFUNC  :load
c:0002 p:0136 s:0006 E:001e10 EVAL   /home/atodorov/.rbenv/versions/2.3.2/bin/rspec:22 [FINISH]
c:0001 p:0000 s:0002 E:0000a0 (none) [FINISH]

Googling for vm_call_cfunc - cfp consistency error yields Ruby #10460. Comments on the bug and particularly this one point towards the error:

> Ruby is trying to be nice about reporting the error; but in the end,
> your code is still broken if it overflows stack.

Somewhere in the test suite was a piece of code that was overflowing the stack. It was somewhere along the lines of

describe '#active_client_for_user' do
  context 'matching an existing user' do
    it_behaves_like 'manager authentication' do
      include_examples 'active client for user with existing user'

Considering the examples in the bug I started looking for patterns where a variable was defined and later redefined, possibly circling back to the previous definition. Expanding the shared examples by hand transformed the code into

describe '#active_client_for_user' do
  context 'matching an existing user' do
    let(:user) { create(:user, :manager) }
    let!(:api_user_authentication) { create(:user_authentication, user: user) }
    let(:user) { api_user_authentication.user }

    context 'with an `active_assigned_client`' do
      ... skip ...

    ... skip ...

Line 5. overrode line 3. When line 4. was executed first because of lazy execution and the call execution path became: 4-5-4-5-4-5 ... NOTE: I think we need a warning about that in RuboCop, see RuboCop #3769. The fix however is a no brainer:

-  let(:user) { create(:user, :manager) }
-  let!(:api_user_authentication) { create(:user_authentication, user: user) }
+  let(:manager) { create(:user, :manager) }
+  let!(:api_user_authentication) { create(:user_authentication, user: manager) }

Thanks for reading and happy testing.

There are comments.

Highlights from ISTA and GTAC 2016

ISTA 2016

Another two weeks have passed and I'm blogging about another 2 conferences. This year both Innovations in Software Technologies and Automation and Google Test Automation Conference happened on the same day. I was attending ISTA in Sofia during the day and watching the live stream of GTAC during the evenings. Here are some of the things that reflected on me:

  • How can I build my software in order to make this a perfect day for the user ?
  • People are not the problem which causes bad software to exist. When designing software focus on what people need not on what technology is forcing them to do;
  • You need to have blind trust in the people you work with because all the times projects look like they are not going to work until the very end!
  • It's good to have diverse set of characters in the company and not homogenize people;
  • Team performance grows over time. Effective teams minimize time waste during bad periods. They (have and) extract value from conflicts!
  • One-on-one meetings are usually like status reports which is bad. Both parties should bring their own issues to the table;
  • To grow an effective team members need to do things together. For example pair programming, writing test scenarios, etc;
  • When teams don't take actions after retrospective meetings it is usually a sign of missing foundational trust;
  • QA engineers need to be present at every step of the software development life-cycle! This is something I teach my students and have been confirmed by many friends in the industry;
  • Agile is all about data, even when it comes to testing and quality. We need to decompose and measure iteratively;
  • Agile is also about really skillful people. One way to boost your skills is to adopt the T-shaped specialist model;
  • In agile iterative work and continuous delivery is king so QA engineers need to focus even more on visualization (I will also add documentation), refactoring and code reviews;
  • Agile teams need to give opportunities to team members for taking risk and taking ownership of their actions in the gray zone (e.g. actions which isn't clear who should be doing).

In the brave new world of micro services end to end testing is no more! We test each level in isolation but keep stable contracts/APIs between levels. That way we can reduce the test burden and still guarantee an acceptable level of risk. This change in software architecture (monolithic vs. micro) leads to change in technologies (one framework/language vs. what's best for the task) which in turn leads to changes in testing approach and testing tools. This ultimately leads to changing people on the team because they now need different skills than when they were hired! This circles back to the T-shaped specialist model and the fact that QA should be integrated in every step of the way! Thanks to Denitsa Evtimova and Lyudmila Labova for this wisdom and the quote pictured above.

Aneta Petkova talked about monitoring of test results which is a topic very close to my work. Imagine you have your automated test suite but still get failures occasionally. Are these bugs or something else broke ? If they are bugs and you are waiting for them to be fixed do you execute the tests against the still broken build or wait ? If you do, what additional info do you get from these executions vs. how much time do you spend figuring out "oh, that's still not fixed or geez, here's another hidden bug in the code" ?

Her team has modified their test execution framework (what I'd usually call a test runner or even test lab) to have knowledge about issues in JIRA and skip some tests when no meaningful information can be extracted from them. I have to point out that this approach may require a lot of maintenance in environments where you have failures due to infrastructure issues. This idea connects very nicely with the general idea behind this year's GTAC - don't run tests if you don't need to aka smart test execution!

Boris Prikhodskiy shared a very simple rule. Don't execute tests

  • which have 100 % pass rate;
  • during the last month;
  • and have been executed at least 100 times before that!

This is what Unity does for their numerous topic branches and reduces test time with 60-70 percent. All of the test suite is still executed against their trunk branch and PR merge queue branches!

At GTAC there were several presentations about speeding up test execution time. Emanuil Slavov was very practical but the most important thing he said was that a fast test suite is the result of many conscious actions which introduced small improvements over time. His team had assigned themselves the task to iteratively improve their test suite performance and at every step of the way they analyzed the existing bottlenecks and experimented with possible solutions.

The steps in particular are (on a single machine):

  • Execute tests in dedicated environment;
  • Start with empty database, not used by anything else; This also leads to adjustments in your test suite architecture and DB setup procedures;
  • Simulate and stub external dependencies like 3rd party services;
  • Move to containers but beware of slow disk I/O;
  • Run database in memory not on disk because it is a temporary DB anyway;
  • Don't clean test data, just trash the entire DB once you're done;
  • Execute tests in parallel which should be the last thing to do!
  • Equalize workload between parallel threads for optimal performance;
  • Upgrade the hardware (RAM, CPU) aka vertical scaling;
  • Add horizontal scaling (probably with a messaging layer);

John Micco and Atif Memon talked about flaky tests at Google:

  • 84% of the transitions from PASS to FAIL are flakes;
  • Almost 16% of their 3.5 million tests have some level of flakiness;
  • Flaky failures frequently block and delay releases;
  • Google spends between 2% and 16% of their CI compute resources re-running flaky tests;
  • Flakiness insertion speed is comparable to flakiness removal speed!
  • The optimal setting is 2 persons modifying the same source file at the same time. This leads to minimal chance of breaking stuff;
  • Fix or delete flaky tests because you don't get meaningful value out of them.

So Google want to stop a test execution before it is executed if historical data shows that the test has attributes of flakiness. The research they talk about utilizes tons of data collected from Google's CI environment which was the most interesting fact for me. Indeed if we use data to decide which features to build for our customers then why not use data to govern the process of testing? In addition to the video you should read John's post Flaky Tests at Google and How We Mitigate Them.

At the end I'd like to finish with Rahul Gopinath's Code Coverage is a Strong Predictor of Test suite Effectiveness in the Real World. He basically said that code coverage metrics as we know them today are still the best practical indicator of how good a test suite is. He argues that mutation testing is slow and only provides additional 4% to a well designed test suite. This is absolutely the opposite of what Laura Inozemtseva presented last year in her Coverage is Not Strongly Correlated with Test Suite Effectiveness lightning talk. Rahul also made a point about sample size in the two research papers and I had the impression he's saying Laura didn't do a proper academic research.

I'm a heavy contributor to Cosmic Ray, the mutation testing tool for Python and also use mutation testing in my daily job so this is a very interesting topic indeed. I've asked fellow tool authors to have a look at both presentations and share their opinions. I also have an idea about a practical experiment to see if full branch coverage and full mutation coverage will be able to find a known bug in a piece of software I wrote. I will be writing about this experiment next week so stay tuned.

Thanks for reading and happy testing!

There are comments.

IT Weekend Highlights

IT Weekend

Last weekend I attended the third IT Weekend. It's like a training camp for athletes but for QA engineers. While during the first week the crowd was more in the junior to mid level range now the crowd was more into the senior level range which made for better talks and discussions. The most interesting sessions for me were On-boarding of New Team Members by Nikola Naidenov and Agile Leadership by Bogoi Bogdanov. Here are some of the highlights that I wrote down:

  • On-boarding of new team members is very important. You need to have a plan for their first 6 months at the company. This plan needs to have clearly defined tasks and expectations;
  • When a person becomes productive for their team/company it means they have been on-boarded successfully;
  • A company provided trainer is a good thing but they tend to focus on broader knowledge, they don't cover team specific domain knowledge;
  • Some companies provide both technical and business trainers for their teams;
  • It is very important to get timely feedback when you are the one providing training. However feedback isn't always easy to get and we don't always receive sincere feedback;
  • If the team is swamped with work tasks you need to provide 10-20% of the time for learning and experimenting with new technologies. IMO this is best done by filing tickets in your bug/task tracking system and prioritizing them together with the rest of the tasks;
  • It is also important to have an individual training plan for each team member and review this on a regular basis;
  • We should strive to use unified terminology and jargon as to not confuse people. IMO it is usually the new hires who are likely to get confused because they are not familiar with the history of the terms used;

In an agile environment we calculate productivity using the formula

Productivity = Effort * Competence * Environment * Motivation^2

There are 3 important factors that drive motivation

  • to have a Purpose
  • to feel Autonomy
  • to be able to achieve Mastery in your skills

It is also important to note that autonomy is not the opposite of alignment as depicted by the image below.

Alignment and autonomy

In agile environment control is a function of trust. To be able to trust people we need to give them autonomy, transparency and short feedback loop!

  • Manage for the normal treat exceptions as exceptional;
  • Failure recovery is more important than failure avoidance;
  • Fail fast means learning fast and improving fast.

Thanks for reading and happy testing!

Photo credit: Rayna Stankova

There are comments.

Animate & Automate

Recently I've attended a presentation by MentorMate where they talked about testing CSS animations ( video in Bulgarian ). The software under test was an ad tech SDK which provides CSS based animations to mobile apps and games. The content is displayed inside a webview and they had to make sure animations were working correctly on different OS and devices.

Analyzing the content (aka getting to know the domain) they figured out in reality there were about 20 basic movements and transformations. So the problem was reduced to "How do we test these 20 basic movements under various OSes and devices" or "How do we verify that basic CSS transformations are supported under different versions and flavors of the OS"?

Their test bed included hand crafted web pages with each basic movement and then several ones with more complex animations (aka integration testing). The idea was to load these pages under different devices and inspect whether or not the animations were visualized properly.

A test script (aka their testing framework) was constantly recording the coordinates of the elements under test to verify that they were really animated. The idea was to use a sample rate of 20ms and expect at lest 20 different changes to the element under test. Coordinates along with color and gradient were recorded and then returned back and analyzed to report a PASS or FAIL result.

This simplistic framework has limitations of course. It is not currently checking the boundaries of where the elements are rendered on the screen. Thus if everything else works as expected this will be a false positive result. On their slides this can be seen at 23:10.

As a side note the entire effort took about 2 days, including research and preparing the test content.

I really like the back to basics approach here and the simplistic framework that MentorMate came up with. Sure it misses some problems but for that particular case it is good enough, easy and fast to implement.

There are comments.

What I Learned from IT Weekend

IT Weekend

Last week I attended the first IT Weekend in Bulgaria. It's like a training camp for athletes but for QA engineers. There were 20 people attending and the format was very friendly and relaxed. The group had members with various levels of experience and technical skills, also different areas they work in. All presentations are on YouTube. Here's a brief of what happened and what I learned.

I had the honor to present in the first slot and gave a quick introduction to mutation testing. This was my first time giving this talk and I'm not entirely happy with how I've presented it. Also mutation testing is touching a lot on unit tests, programming and source code which in some organizations goes to the devel department. I think mutation testing is harder to understand from people not familiar with it than I initially thought. I'm taking note to improve the way I present this topic to the public.

Yavor Donev gave a good overview of Appium and how to use it on Android. The most important question for me was "Is it possible to utilize the same test suite on Android and iOS, given that the environments are different". With this I mean regardless of how much we try to make the same (native) app on both platforms it will end up differently because the platforms are essentially different. For example there is a different number of physical buttons available.

If we assume that both iOS and Android apps follow the same design and use similar workflow then it should be possible to create a test suite which is platform aware and account for the minor differences. We're also adding another layer of complexity by introducing the requirement that both apps stay in sync with each other and account for the quirks of the foreign platform. Depending on your apps and goals this may not be an easy task!

The one thing I didn't like about Appium is that upstream doesn't care much about version compatibility and they tend to break and change stuff arbitrary between releases. That said if it works, don't update it or otherwise be extremely careful.

I also had a nice chat with Yavor on the topic of career change, learning to program and working with people who have very little coding experience. His approach is to develop a higher level test framework on top of Appium which his team mates can use more easily.

Aneta Petkova's Selenium Grid in Unix Environment is a bit out of my domain. However I took one important lesson: regardless of how great your tools are there are minor details which can make or break your day. In her case these are the physical location of the tests (e.g. which Selenium node runs them) and access to shared resources. Turns out WebDriver doesn't give you this information directly and you need to go through hoops to get it. Her solution was to place the test code on the Grid Hub and provide a shared file system.

The bigger lesson is: whenever you have to design an automated test environment (aka test lab) make sure to evaluate your needs beforehand.

The last talk was a guest appearance by Denitsa Evtimova. She is a QA architect with 16 years of experience and presented the QA strategy at Paysafe group. They have a large monolithic system (legacy code) and have adopted a pyramid style approach to testing. Whenever possible tests are brought down to the lowest level (e.g. unit tests) and not repeated on the higher levels. At the top stand manual testing. Teams are small: 3-4 developers and 2-3 QAs. It is the team responsibility to make sure tests are implemented at the lowest possible level. The process is not strictly enforced and the company relies more on self governance in this aspect. Also everyone on the team can contribute additional tests whenever they see something missing. Test (writing) tasks are all logged in JIRA. They are also small so that everything can be completed in the same day.

The second day was more informal. We did a quick exploratory testing exercise and shared opinions on different test tools. Then the group had a discussion about soft skills and how QA engineers can change the perception of developers about the QA profession (especially in teams where there are many manual testers). The key points are:

  • Criticize the software, not the person, e.g. don't blame the person directly;
  • Communicate with concrete facts and data, not emotions and perceptions;
  • Jokes of the type "how many QA engineers are needed to screw a light bulb" are a problem because they lead to underestimation of the job role;
  • Sometimes it is not quite clear (to others) how the QA role contributes to the development of the product and the organization;
  • For a QA it is important to be able to give a non-biased opinion and observations on what is happening with the product/process;
  • A QA person needs to be very calm. They have to be able to listen to everybody (especially developers) and accept their point of view but at the same time also communicate their own point of view.
  • It is important to sit together with developers and observe the problem, brainstorm and propose possible solutions. This also creates a feedback loop where the developer feels empowered because he's part of the process identifying the problem and proposing the best solution;
  • In agile teams it is a good idea to rotate people between developer and QA positions. This will help them better understand the job of others, acquire new skills and also bring fresh thinking to the team;
  • Quality Assurance is an ungrateful job and only people with very calm and methodical thinking (to follow through and write all possible scenarios) are able to excel in this field. On the other hand developer usually think about the happy path scenarios and strive to make their code work as best as they can;
  • By rotating job roles within the team developers will quickly find out that testing is not their field and gain respect towards their QA peers;
  • US managers have the habit of telling "good job" to everyone, even for small and routine tasks. In Bulgaria (and maybe elsewhere) we're not used to this. Instead we're used of being scolded when we do something wrong. If everything is good then we don't receive any recognition;
  • Using the American "good job" is actually a good thing. Team mates will start performing better over time because they will feel their work is valued and not meaningless, they will feel recognized which will boost morale and productivity.

Thanks for reading and happy testing!

There are comments.

Python 2 vs. Python 3 List Sort Causes Bugs

Can sorting a list of values crash your software? Apparently it can and is another example of my Hello World Bugs. Python 3 has simplified the rules for ordering comparisons which changes the behavior of sorting lists when their contents are dictionaries. For example:

Python 2.7.5 (default, Oct 11 2015, 17:47:16) 
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux2
>>> [{'a':1}, {'b':2}] < [{'a':1}, {'b':2, 'c':3}]
Python 3.5.1 (default, Apr 27 2016, 04:21:56) 
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux
>>> [{'a':1}, {'b':2}] < [{'a':1}, {'b':2, 'c':3}]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unorderable types: dict() < dict()

The problem is that the second elements in both lists have different keys and Python doesn't know how to compare them. In earlier Python versions this has been special cased as described here by Ned Batchelder (the author of Python's coverage tool) but in Python 3 dictionaries have no natural sort order.

In the case of django-chartit (of which I'm now the official maintainer) this bug triggers when you want to plot data from multiple sources (models) on the same chart. In this case the fields coming from each data series are different and the above error is triggered.

I have worked around this in commit 9d9033e by simply disabling an iterator sort but this is sub-optimal and I'm not quite certain what the side effect might be. I suspect you may end up with a chart where the order of values on the X axis isn't the same for the different models, e.g. one graph plotting the data in ascending order the other one in descending.

The trouble also comes from the fact that we're sorting an iterator (a list of fields) by telling Python to use a list of dicts to determine the sort order. In this arrangement there is no way to tell Python how we want to compare our dicts. The only solution I can think about is creating a custom class and implementing a custom __cmp__() method for this data structure!

There are comments.

PhantomJS 2.1.1 in Ubuntu different from upstream

For some time now I've been hitting PhantomJS #12506 with the latest 2.1.1 version. The problem is supposedly fixed in 2.1.0 but this is not always the case. If you use a .deb package from the latest Ubuntu then the problem still exists, see Ubuntu #1605628.

It turns out the root cause of this, and probably other problems, is the way PhantomJS packages are built. Ubuntu builds the package against their stock Qt5WebKit libraries which leads to

$ ldd usr/lib/phantomjs/phantomjs | grep -i qt
    libQt5WebKitWidgets.so.5 => /lib64/libQt5WebKitWidgets.so.5 (0x00007f5173ebf000)
    libQt5PrintSupport.so.5 => /lib64/libQt5PrintSupport.so.5 (0x00007f5173e4d000)
    libQt5Widgets.so.5 => /lib64/libQt5Widgets.so.5 (0x00007f51737b6000)
    libQt5WebKit.so.5 => /lib64/libQt5WebKit.so.5 (0x00007f5171342000)
    libQt5Gui.so.5 => /lib64/libQt5Gui.so.5 (0x00007f5170df8000)
    libQt5Network.so.5 => /lib64/libQt5Network.so.5 (0x00007f5170c9a000)
    libQt5Core.so.5 => /lib64/libQt5Core.so.5 (0x00007f517080d000)
    libQt5Sensors.so.5 => /lib64/libQt5Sensors.so.5 (0x00007f516b218000)
    libQt5Positioning.so.5 => /lib64/libQt5Positioning.so.5 (0x00007f516b1d7000)
    libQt5OpenGL.so.5 => /lib64/libQt5OpenGL.so.5 (0x00007f516b17c000)
    libQt5Sql.so.5 => /lib64/libQt5Sql.so.5 (0x00007f516b136000)
    libQt5Quick.so.5 => /lib64/libQt5Quick.so.5 (0x00007f5169dad000)
    libQt5Qml.so.5 => /lib64/libQt5Qml.so.5 (0x00007f5169999000)
    libQt5WebChannel.so.5 => /lib64/libQt5WebChannel.so.5 (0x00007f5169978000)

While building from the upstream sources gives

$ ldd /tmp/bin/phantomjs | grep -i qt

If you take a closer look at PhantomJS's sources you will notice there are 3 git submodules in their repository - 3rdparty, qtbase and qtwebkit. Then in their build.py you can clearly see that this local fork of QtWebKit is built first, then the phantomjs binary is built against it.

The problem is that these custom forks include additional patches to make WebKit suitable for Phantom's needs. And these patches are not available in the stock WebKit library that Ubuntu uses.

Yes, that's correct. We need additional functionality that vanilla QtWebKit doesn't have. That's why we use custom version.

Vitaly Slobodin, PhantomJS

At the moment of this writing Vitaly's qtwebkit fork is 28 commits ahead and 39 commits behind qt:dev. I'm surprised Ubuntu's PhantomJS even works.

The solution IMO is to bundle the additional sources into the src.deb package and use the same building procedure as upstream.

There are comments.

On Python Infinite Loops

How do you write an endless loop without using True, False, number constants and comparison operators in Python ?

I've been working on the mutation test tool Cosmic Ray and discovered that it was missing a boolean replacement operator, that is an operator which will switch True to False and vice versa, so I wrote one. I've also added some tests to Cosmic Ray's test suite and then I hit the infinite loop problem. CR's test suite contains the following code inside a module called adam.py

while True:

The test suite executes mutations on adam.py and then runs some tests which it expects to fail. During execution one of the mutations is replace break with continue which makes the above loop infinite. The test suite times out after a while and kills the mutation. Everything fails as expected and we're good.

Adding my boolean replacement operator broke this function. All of the other mutations work as expected but then the loop becomes

while False:

When we test this particular mutation there is no infinite loop so Cosmic Ray's test suite doesn't time out like it should and an error is reported.

job ID 25:Outcome.SURVIVED:adam
command: cosmic-ray worker adam boolean_replacer 2 unittest -- tests
--- mutation diff ---
--- a/home/travis/build/MrSenko/cosmic-ray/test_project/adam.py
+++ b/home/travis/build/MrSenko/cosmic-ray/test_project/adam.py
@@ -32,6 +32,6 @@
     return x
 def trigger_infinite_loop():
-    while True:
+    while False:

So the question becomes how to write the loop condition in such a way that nothing will mutate it but it will still remain true so that when break becomes continue this piece of code will become an infinite loop ? Using True or False constants obviously is a no go. Same goes for numeric constants, e.g. 1 or comparison operators like >, <, is, not, etc. - all of them will be mutated and will break the loop condition.

So I took a look at the docs for truth value testing and discovered my solution:

while object():

I'm creating an object instance here which will not be mutated by any of the existing mutation operators.

Thanks for reading and happy testing!

There are comments.

Bug in TuxCon Website

TuxCon bug

Here comes July 9th 2016 and the start of TuxCon ... with a bug on their website! The image above is taken during the first talk of the conference. Obviously the count down timer is completely off.

In init.js:100 there is this piece of code

var finalDate = '2016/07/09';

.on('update.countdown', function(event) {
    $(this).html(event.strftime('<span>%D <em>days</em></span>' +
                                '<span>%H <em>hours</em></span>' +
                                '<span>%M <em>minutes</em></span>' +
                                '<span>%S <em>seconds</em></span>'));

It counts backwards and updates the HTML until finalDate is reached. Then the HTML is no longer updated and the default values are shown, which in this case are non zero. A simple patch fixes the problem.

Initialize your variables properly and happy testing!

There are comments.

Testing the 8-bit computer Puldin

Puldin creators

Last weekend I visited TuxCon in Plovdiv and was very happy to meet and talk to some of the creators of the Puldin computer! On the picture above are (left to right) Dimitar Georgiev - wrote the text editor, Ivo Nenov - BIOS, DOS and core OS developer, Nedyalko Todorov - director of the vendor company and Orlin Shopov - BIOS, DOS, compiler and core OS developer.

Puldin is 100% pure Bulgarian development, while the “Pravetz” brand was copy of Apple ][ (Pravetz 8A, 8C, 8M), Oric (Pravets 8D) and IBM-PC (Pravetz 16). The Puldin computers were build from scratch both hardware and software and were produced in Plovdiv in the late 80s and early 90s. 50000 pieces were made, at least 35000 of them have been exported to Russia and paid for. A typical configuration in a Russian class room consisted of several Puldin computers and a single Pravetz 16. According to Russian sources the last usage of these computers was in 2003 serving as Linux terminals and being maintained without any support from the vendor (b/c it ceased to exist).

Puldin 601

One of the main objectives of Puldin was full compatibility with IBM-PC. At the time IBM had been releasing extensive documentation about how their software and hardware works which has been used by Puldin's creators as their software specs. Despite IBM-PC using faster CPU the Puldin 601 had a comparable performance due to aggressive software and compiler optimizations.

Testing wise the guys used to compare Puldin's functionality with that of IBM-PC. It was a hard requirement to have full compatibility on the file storage layer, that means floppy disks written on Puldin had to be readable on IBM-PC and vice versa. Same goes for programs compiled on Puldin - they had to execute on IBM-PC.

Everything of course had been tested manually and on top of that all the software had to be burned to ROM before you can do anything with it. As you can imagine the testing process had been quite slow and painful compared to today's standards. I've asked the guys if they'd happened to find a bug in IBM-PC which wasn't present in their code but they couldn't remember.

What was interesting for me on the hardware side was the fact that you can plug the computer directly to a cheap TV set and that it's been one of the first computers which could operate on 12V DC, powered directly from a car battery.

Pravetz 8

There was also a fully functional Pravetz 8 with an additional VGA port to connect it to the LCD monitor as well as a SD card reader wired to function as a floppy disk reader (the small black dot behind the joystick).

For those who missed it (and understand Bulgarian) I have a video recording on YouTube. For more info about the history and the hardware please check-out Olimex post on Puldin (in English). For more info on Puldin and Pravetz please visit pyldin.info (in Russian) and pravetz8.com (in Bulgarian) using Google translate if need be.

There are comments.

Testing Data Structures in Pykickstart

When designing automated test cases we often think either about increasing coverage or in terms of testing more use-cases aka behavior scenarios. Both are valid approaches to improve testing and both of them seem to focus around execution control flow (or business logic). However program behavior is sometimes controlled via the contents of its data structures and this is something which is rarely tested.

In this comment Brian C. Lane and Vratislav Podzimek from Red Hat are talking about a data structure which maps Fedora versions to particular implementations of kickstart commands. For example

class RHEL7Handler(BaseHandler):
    version = RHEL7

    commandMap = {
        "auth": commands.authconfig.FC3_Authconfig,
        "authconfig": commands.authconfig.FC3_Authconfig,
        "autopart": commands.autopart.F20_AutoPart,
        "autostep": commands.autostep.FC3_AutoStep,
        "bootloader": commands.bootloader.RHEL7_Bootloader,

In their particular case the Fedora 21 logvol implementation introduced the --profile parameter but in Fedora 22 and Fedora 23 the logvol command mapped to the Fedora 20 implementation and the --profile parameter wasn't available. This is unexpected change in program behavior although the logvol.py and handlers/f22.py files have 99% and 100% code coverage.

This morning I did some coding and created an automated test for this problem. The test iterates over all command maps. For each command in the map (that is data structure member) we load the module which provides all possible implementations for that command. In the loaded module we search for implementations which have newer versions than what is in the map, but not newer than the current Fedora version under test. With a little bit of pruning the current list of offenses is

ERROR: In `handlers/devel.py` the "fcoe" command maps to "F13_Fcoe" while in
`pykickstart.commands.fcoe` there is newer implementation: "RHEL7_Fcoe".

ERROR: In `handlers/devel.py` "FcoeData" maps to "F13_FcoeData" while in
`pykickstart.commands.fcoe` there is newer implementation: "RHEL7_FcoeData".

ERROR: In `handlers/devel.py` the "user" command maps to "F19_User" while in
`pykickstart.commands.user` there is newer implementation: "F24_User".

ERROR: In `handlers/f24.py` the "user" command maps to "F19_User" while in
`pykickstart.commands.user` there is newer implementation: "F24_User".

ERROR: In `handlers/f22.py` the "logvol" command maps to "F20_LogVol" while in
`pykickstart.commands.logvol` there is newer implementation: "F21_LogVol".

ERROR: In `handlers/f22.py` "LogVolData" maps to "F20_LogVolData" while in
`pykickstart.commands.logvol` there is newer implementation: "F21_LogVolData".

ERROR: In `handlers/f18.py` the "network" command maps to "F16_Network" while in
`pykickstart.commands.network` there is newer implementation: "F18_Network".

The first two are possibly false negatives or related to the naming conventions used in this module. However the rest appear to be legitimate problems. The user command has introduced the --groups parameter in Fedora 24 (devel is Fedora 25 currently) but the parser will fail to recognize this parameter. The logvol problem is recognized as well since it was never patched. And the Fedora 18 network command implements a new property called hostname which has probably never been available to be used.

You can follow my current work in PR #91 and happy testing your data structures.

There are comments.

Don't Upgrade Galaxy S5 to Android 6.0

Samsung is shipping out buggy software like a boss, no doubt about it. I've written a bit about their bugs previously. However I didn't expect them to release Android 6.0.1 and render my Galaxy S5 completely useless with respect to the feature I use the most.


Tell me the weather for Brussels

So on Monday I've let Android upgrade to 6.0.1 to be completely surprised that the lockscreen shows the weather report for Brussels, while I'm based in Sofia. I've checked AccuWeather (I did go to Brussels earlier this year) but it displayed only Sofia and Thessaloniki. To get rid of this widget go to Settings -> Lockscreen -> Additional information and turn it off!

I think this weather report comes from GPS/Location based data, which I have turned off by default but did use a while back ago. After turning the widget off and back on it didn't appear on the lockscreen. I suspect they fall back to showing the last good known value when data is missing instead of handling the error properly.

Apps are gone

Some of my installed apps are missing now. So far I've noticed that the Gallery and S Health icons have disappeared from my homescreen. I think S Health came from Samsung's app store but still they shouldn't have removed it silently. Now I wonder what happened to my data.

I don't see why Gallery was removed though. The only way to view pictures is to use the camera app preview functionality which is kind of grose.

Grayscale in powersafe mode is gone

The killer feature on these higher end Galaxy devices is the Powersafe mode and Ultra Powersafe mode. I use them a lot and by default have my phone in Powersafe mode with grayscale colors enabled. It is easier on the eyes and also safes your battery.

NOTE: grayscale colors don't affect some displays but these devices use AMOLED screens which need different amounts of power to display different colors. More black means less power required!

After the upgrade grayscale is no more. There's not even an on/off switch. I've managed to find a workaround though. First you need to enable developer mode by tapping 7 times on About device -> Build number. Then go to Settings -> Developer options, look for the Hardware Accelerated Rendering section and select Simulate Color Space -> Monochromacy! This is a bit ugly hack and doesn't have the convenience of turning colors on/off by tapping the quick Powersafe mode button at the top of the screen!

It looks like Samsung didn't think this upgrade well enough or didn't test it well enough ? In my line of work (installation and upgrade testing) I've rarely seen such a big blunder. Thanks for reading and happy testing!

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How To Hire Software Testers, Pt. 3

In previous posts (links below) I have described my process of interviewing QA candidates. Today I'm quoting an excerpt from the book Mission: My IT career(Bulgarian only) by Ivaylo Hristov, one of Komfo's co-founders.

Fedora pen

He writes

Probably the most important personal trait of a QA engineer is to
be able to think outside given boundaries and prejudices
(about software that is). When necessary to be non-conventional and
apply different approaches to the problems being solved. This will help
them find defect which nobody else will notice.

Most often errors/mistakes in software development are made due to
wrong expectations or wrong assumptions. Very often this happens because
developers hope their software will be used in one particular way
(as it was designed to) or that a particular set of data will be returned.
Thus the skill to think outside the box is the most important skill
we (as employers) are looking to find in a QA candidate. At job interviews
you can expect to be given tasks and questions which examine those skills.

How would you test a pen?

This is Ivaylo's favorite question for QA candidates. He's looking for attention to details and knowing when to stop testing. Some of the possible answers related to core functionality are

  • Does the pen write in the correct color
  • Does the color fades over time
  • Does the pen operate normally at various temperatures? What temperature intervals would you choose for testing
  • Does the pen operate normally at various atmospheric pressure
  • When writing, does the pen leave excessive ink
  • When writing, do you get a continuous line or not
  • What pressure does the user need to apply in order to write a continuous line
  • What surfaces can the pen write on? What surfaces would you test
  • Are you able to write on a piece of paper if there is something soft underneath
  • What is the maximum inclination angle at which the pen is able to write without problems
  • Does the ink dry fast
  • If we spill different liquids onto a sheet of paper, on which we had written something, does the ink stay intact or smear
  • Can you use pencil rubber to erase the ink? What else would you test
  • How long can you write before we run out of ink
  • How fat is the ink line

Then Ivaylo gives a few more non-obvious answers

  • Verify that all labels on the pen/ink cartridge are correctly spelled and how durable they are (try to erase them)
  • Strength test - what is the maximum height you can drop the pen from without breaking it
  • Verify that dimensions are correct
  • Test if the pen keeps writing after not being used for some time (how long)
  • Testing individual pen components under different temperature and atmospheric conditions
  • Verify that materials used to make the pen are safe, e.g. when you put the pen in your mouth

When should you stop ? According to the book there can be between 50 and 100 test cases for a single pen, maybe more. It's not a good sign if you stop at the first 3!

If you want to know what skills are revealed via these questions please read my other posts on the topic:

Thanks for reading and happy testing!

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