JUnit: using constructor instead of @Before

constructor junit initialization
vbence picture vbence · May 23, 2011 · Viewed 44.7k times · Source

I'm using JUnit 4. I can't see the difference between initializing in the constructor or using a dedicated init function annotated by @Before. Does this mean that I don't have to worry about it?

Is there any case when @Before gives more than just initializing in the constructor?

Answer

Péter Török picture Péter Török · May 23, 2011

No, using the constructor to initialize your JUnit test fixture is technically equal to using the @Before method (due to the fact that JUnit creates a new instance of the testing class for each @Test). The only (connotational) difference is that it breaks the symmetry between @Before and @After, which may be confusing for some. IMHO it is better to adhere to conventions (which is using @Before).

Note also that prior to JUnit 4 and annotations, there were dedicated setUp() and tearDown() methods - the @Before and @After annotations replace these, but preserve the underlying logic. So using the annotations also makes life easier for someone migrating from JUnit 3 or earlier versions.

Notable differences

More details from comments:

  • @Before allows overriding parent class behavior, constructors force you to call parent class constructors
  • The constructor runs before subclass constructors and @Rule methods, @Before runs after all of those
  • Exceptions during @Before cause @After methods to be called, Exceptions in constructor don't

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