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Unit Testing–What to Test

October 9, 2013 by kiranbadi1991 | Filed under Development, Others, Quality, Testing.

One of the frequent discussions I often get into with developers especially in agile projects is how to write the test case for the class or method and what should we be testing in the unit tests.

There seems to be difference in opinion among folks as what unit test case needs to cover? Or what should we be testing with unit tests?

Should we write the test for both positive and negative input values or should we write the test that shows the code is just enough working? Or should we write the test case for all the possibilities that the code is going to fail or it’s going to be used?

All of these questions seems to be perfectly valid and there isn’t a single right answers to it. However based on my experience and little bit of wisdom, I can say that if you are working with experienced veteran programmer, then probably he will suggest that we write test cases for all possibilities and if you are part of team where everyone is young or most of them are in their midlife, then probably they will not be bothered and will ask you to write tests that shows the code is working as expected. I don’t think there is anything wrong with this approach either, however I feel it’s good that more unit tests we write, better the shape of project in the downstream phases, however this needs to be done correctly and results should be obviously visible. It does not make sense that we do unit testing for every piece of code flow and there are thousands of defects logged by the QA in the later phase. This just don’t make sense economically nor from the management prospective.

So probably I will focus on areas which I feel developers need to focus in their unit testing in this post without getting themselves buried in the art of functional testing,

There are infinite number of ways the code might fail, it might fail due to environmental changes, code might fail due to data changes or it might fail due to real bug in it. All these conditions happens all the time in various environment. So it’s practically not possible to know the failure mode beforehand. However being the developer of the code, we do assume that our code will be working will be working certain fixed environment with certain fixed perquisites for it to run. So it’s always better that we do some assumption and use our time judiciously for writing tests which reflects real time behavior.

I would suggest each of the unit tests exercised on the code under test should minimum show that.

  • The output given the code is correct and it does give us expected results.
  • Extreme boundary conditions for the input values are handled correctly.
  • Error handling is done appropriately by the code.
  • Tests should exercise the performance of the code under test

Maybe in next post I will come up with proper example to show as how to prepare test cases for each of the above conditions. We need to ensure that our unit tests are lean and thin in nature and we need to test just enough code.

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