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- Mock out all external services and states[SE2]
Otherwise, behavior in those external services overlaps multiple tests, and state data means that different unit tests can influence each other’s outcome. You’ve definitely taken a wrong turn if you have to run your tests in a specific order, or if they only work when your database or network connection is active.
Also, this is important because you would not love to debug the test cases that are actually failing due to bugs in some external system.
(By the way, sometimes your architecture might mean your code touches static variables during unit tests. Avoid this if you can, but if you can’t, at least make sure each test resets the relevant statics to a known state before it runs.)
- Name your unit tests clearly and consistently
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