Are you a Tester? Expect the Unexpected!

What do you expect while testing? Many testers believe that while testing, we should expect some output and compare the actual output with the expected one! If they match then the test case passes else it fails. Quite simple and straightforward, isn’t it? I would say No! I wish testing was so simple!

What characterizes a formal, written test case is that there is a known input and an expected output, which is worked out before the test is executed. The known input should test a precondition and the expected output should test a postcondition. -

The above is the description of a test case from Wikipedia. And I am NOT going to challenge the definition of a test case in this post. If anyone expected (did I use “expect”?) such a post, please excuse me. :)

I am NOT against how we define a test case. But I am not sure if I really like the way we use/treat test cases! I agree that we should expect some kind of output (can be a part of a requirement or use case etc) while testing a product. But following a strict suite of pre-defined test case (be it manual or automated) might result in Inattentional blindness!

Inattentional blindness, closely related to the subject of change blindness, is an observed phenomenon of the inability to perceive features in a visual scene when the observer is not attending to them. That is to say that humans have a limited capacity for attention which thus limits the amount of information processed at any particular time. Any otherwise salient feature within the visual field will not be observed if not processed by attention. -
Inattentional blindness

Watch the above video for a demonstration of Inattentional blindness. Same can happen to a tester who is looking out for an expected behavior while testing. There were instances when I had missed out obvious and simple to find bugs because I was looking for some complex behavior. From my own experience I have learnt that in addition to expected behaviors (passing of ball!) we should also keep our eyes and ears open to other unexpected behaviors (the gorilla!) that might be taking place while conducting the test. Test cases might find us those bugs which we had planned to dig out. But I am not sure if they could find us any new bugs that might be lurking in the vicinity! So while testing, better to expect the unexpected and act accordingly before we miss another obvious looking bug! By the way, after all no tester would like his manager/client to find such a bug!

Happy Testing...
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About Debasis Pradhan

Debasis has over a decade worth of exclusive experience in the field of Software Quality Assurance, Software Development and Testing. He writes here to share some of his interesting experiences with fellow testers.


  1. I must appreciate you for this post. The kind of self learning that you have been putting to yourself is quite interesting for me.

    The value of this post is visible only to those who are passionate about testing, in my opinion.

    Wonderful going but don't get carried away. Push more hard and let me know of the support you might need.

  2. @ Pradeep,

    Thanks a ton for those encouraging words. But, this is just a beginning. I have a long way to go. I can't stop and have to keep moving fast as my destination is still too far away! I would be seeking guidance and advice from well-wishers like you from time to time. I have been really blessed to have few mentors like you and I am always grateful to god for that. Thanks once again!


  3. The Umpires:
    In S/W testing, End Users are the umpires...

    Great Article...really enjoyed. Thanx!

  4. O O.... the comment was for the other article... Assigned to the wrong developer ;)


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