The Pesticide Paradox in Testing: If you want a different result, do something different!

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What I learnt from Katie…

I read this book a couple of months ago about a poor girl, Katie, who always had had bad luck with guys: one boyfriend borrowed all her money and disappeared to Mexico, another one two-timed her and her last couple used her to paint his apartment. She was so devastated that she thought she would never find anyone nice and decided to give up. But her best friend tried to stop her and gave her this advice: go to have lunch to a different place, somewhere completely different and maybe you’ll meet someone there, someone who could become the one. And so she did. She did something different and met someone completely opposite to the losers she dated before. This way she could finally be happy.

Being honest, this book is not a masterpiece, but it made me remember one of the seven testing principles according to ISTQB: the pesticide paradox. This principle states that if the same tests are repeated over and over again, they will no longer find any new defects. That is, if we always use the same test cases, the software will become immune to them, all the bugs that those tests would find will be exposed and we won’t be able to uncover new bugs.

If you want a different result, dare to be different…

If we expect to have a different result and maintain the effectiveness and efficacy of our test cases, they need to be regularly revised and updated, and

Dare to be different

we have to write new and different tests in order to exercise different parts of the application to find more defects. And sometimes it is also important to identify those test cases that have failed to detect any defect and remove them from our test plan, so that it doesn’t grow to infinity and beyond and we don’t waste time running those ineffective test cases.

Just as developers make the code better when correcting bugs, testers have to make the test cases better. This way, we could find those resistant bugs against which our initial test cases are ineffective and those subtler bugs that have been introduced to the system as a result of the correction of the former ones.

Additionally, it is important not to rely solely on structured and formal test techniques, but to perform exploratory testing, error guessing or another informal approach to increase the chances of capturing new bugs. The most variety of test techniques and methods the better.

To wrap things up, we as testers, should remember that if we do the usual thing, we get the usual result. So, we have to act like Katie and do something different to have a different result. If we do this, we can rely more on our test results and assure that we have find the greatest possible number of defects (since it is very difficult to find all of them).

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