I’m writing unit tests for a project (written in PHP, using PHPUnit) that have its entire environment (loaded components, events, configuration, cache, per-environment singletons, etc) held in an object which all the components use to interact with each other (using a mediator pattern).
In order to make the unit tests run faster, I’m sharing the environment object and some other objects (for example, in my test case for view object [as in the V of MVC], the view manager object [which acts as a factory for view objects and responsible for the actual rendering]) among tests in the same test case (using PHPUnit’s setUpBeforeClass() and static properties).
Even though, to the best of my knowledge, the objects I share shouldn’t effect the integrity of the tests (in the views case, for example, the environment and view manager object are shared, but a separate view object is created for every test – which is the object that’s actually being tested by the test case), it just feels increasingly wrong to me.
I would prefer it if each test used a completely isolated environment and couldn’t effect other tests in the same test case in any way. However, that would make the tests run much slower and it feels like a big price for something that I can’t really pinpoint the downside of and mainly just “feels wrong”.
What do you think? Can you pinpoint any downsides so I can convince myself its worth the longer execution time? Or am I just over reacting and its completely fine?
Like writing “normal” code, when you write test cases, it’s fine to rely on knowledge of how fixture objects work.
If a given factory method is documented as generating new instances every time, then I see only downside in creating the factory method anew each time, especially if the factory creation is itself expensive.
It helps to keep in mind a key goal around writing unit tests. You want to know within 5-10 minutes whether you broke the build. That way you can go out to lunch, go to a meeting, go home, etc. after you get the “all clear”. If you know that some part of the fixture is reusable without creating interactions, then you should use that knowledge to make your tests even more comprehensive within that 5-10 minute window. I understand the purist impulse here, but it buys you nothing in terms of test independence, and it unnecessarily limits what your test suite will accomplish for you.