Why must jUnit's fixtureSetup be static?

ripper234_11236 0
Viewed 54480

I marked a method with jUnit's @BeforeClass annotation, and got this exception saying it must be static. What's the rationale? This forces all my init to be on static fields, for no good reason as far as I see.

In .Net (NUnit), this is not the case.

Edit - the fact that a method annotated with @BeforeClass runs only once has nothing to do with it being a static method - one can have a non-static method run only once (as in NUnit).

junit java
8 Answers

JUnit documentation seems scarce, but I'll guess: perhaps JUnit creates a new instance of your test class before running each test case, so the only way for your "fixture" state to persist across runs is to have it be static, which can be enforced by making sure your fixtureSetup (@BeforeClass method) is static.

Blair_Conrad_11990

there are two types of annotations:

  • @BeforeClass (@AfterClass) called once per test class
  • @Before (and @After) called before each test

so @BeforeClass must be declared static because it is called once. You should also consider that being static is the only way to ensure proper "state" propagation between tests (JUnit model imposes one test instance per @Test) and, since in Java only static methods can access static data... @BeforeClass and @AfterClass can be applied only to static methods.

This example test should clarify @BeforeClass vs @Before usage:

public class OrderTest {

    @BeforeClass
    public static void beforeClass() {
        System.out.println("before class");
    }

    @AfterClass
    public static void afterClass() {
        System.out.println("after class");
    }

    @Before
    public void before() {
        System.out.println("before");
    }

    @After
    public void after() {
        System.out.println("after");
    }    

    @Test
    public void test1() {
        System.out.println("test 1");
    }

    @Test
    public void test2() {
        System.out.println("test 2");
    }
}

output:

------------- Standard Output ---------------
before class
before
test 1
after
before
test 2
after
after class
------------- ---------------- ---------------
user_892660
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