JUnit Best Practice: Different Fixtures for each @Test

Question

Hi

I understand that there are @Before and @BeforeClass, which are used to define fixtures for the @Test's. But what should I use if I need different fixtures for each @Test?

• Should I define the fixture in the @Test?
• Should I create a test class for each @Test?

I am asking for the best practices here, since both solutions aren't clean in my opinion. With the first solution, I would test the initialization code. And with the second solution I would break the "one test class for each class" pattern.

Answer 1

I would suggest to create a separate Class based on the different fixtures you need. If you have two different fixtures you need just create two different classes (give them a convenient name). But i would think a second time about that, in particular about the difference in the fixtures and why are the different. May be you are on the way to a kind of integration test instead of unit test?

Answer 2

If you are positive that your fixture is unique to single test then it belongs to @Test method. This is not typical though. It could be that some part of it is unique or you didn't parametrize/extracted it right, but typically you will share a lot of the same data between tests.

Ultimately fixture is part of the test. Placing fixture in @Before was adopted as xUnit pattern because tests always:

1. prepare test data/mocks
2. perform operations with SUT
3. validate/assert state/behavior
4. destroy test data/mocks

and steps 1 (@Before) and 4 (@After) are reused a lot (at least partially) in related tests. Since xUnit is very serious about test independence it offers fixture methods to guarantee that they always run and test data created/destroyed properly.

Answer 3

Tips:

1. Forget the one test class per class pattern, it has little merit. Switch to one test class per usage perspective.
2. Remember that JUnit will create an instance of the test class for each @Test, so each test will get a distinct fixture (set up by the same @Before methods). If you need a dissimilar fixture you need a different test, because you are in a different perspective (see 1.)
3. There is nothing wrong with tweaking the fixture for a particular test, but you should try to keep the test clean so it tells a story.