Unit test – purist versus practical


Whenever you ask a question on unit testing in a forum, there is always that one person whose only job is to point out what you are doing is not unit testing but integration testing. It is important to know the difference but it is more important to not lose sight of the goal, ensuring a reliable and a bug-free application. Also, you need to adopt a terminology that works for you and your team, rather than what purists think or say.

In absolute terms, if a test depends on anything that is not in your control, it is not a unit test. For example, if a method that you are testing uses a public function, a method from an included library, database or an external API, it is not a unit test but an integration test. For a test to qualify as a unit test, you need to mock all these dependencies and get them under your control, only then you can claim your test as a unit test. Now that we have the purists happy, let us move to a more practical worldview.

When a regular joe developer refers to a test as a unit test, what she means is, she is trying to test a functionality in a massive gnarly application that she thinks is a small independent unit. This unit might have some components that are not under her control. Instead of debating whether she is unit testing or integration testing, a better discussion is trying to figure out what is the intention of the test, what needs to be controlled/mocked and not. Helping her to figure this out and achieving this will add more value than debating whether a test is a unit test or integration test.

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