Difference between @Before, @BeforeClass, @BeforeEach and @BeforeAll

java junit annotations junit4 junit5
user1170330 picture user1170330 · Nov 30, 2013 · Viewed 289k times · Source

What is the main difference between

  • @Before and @BeforeClass
    • and in JUnit 5 @BeforeEach and @BeforeAll
  • @After and @AfterClass

According to the JUnit Api @Before is used in the following case:

When writing tests, it is common to find that several tests need similar objects created before they can run.

Whereas @BeforeClass can be used to establish a database connection. But couldn't @Before do the same?

Answer

Sergey Kalinichenko picture Sergey Kalinichenko · Nov 30, 2013

The code marked @Before is executed before each test, while @BeforeClass runs once before the entire test fixture. If your test class has ten tests, @Before code will be executed ten times, but @BeforeClass will be executed only once.

In general, you use @BeforeClass when multiple tests need to share the same computationally expensive setup code. Establishing a database connection falls into this category. You can move code from @BeforeClass into @Before, but your test run may take longer. Note that the code marked @BeforeClass is run as static initializer, therefore it will run before the class instance of your test fixture is created.

In JUnit 5, the tags @BeforeEach and @BeforeAll are the equivalents of @Before and @BeforeClass in JUnit 4. Their names are a bit more indicative of when they run, loosely interpreted: 'before each tests' and 'once before all tests'.

Related questions

annotation to make a private method public only for test classes

Who has a solution for that common need. I have a class in my application. some methods are public, as they are part of the api, and some are private, as they for internal use of making the internal flow …

Read More
JUnit @Test expected annotation not working

I've got the following test: @Test(expected = IllegalStateException.class) public void testKey() { int key = 1; this.finder(key); } But JUnit reports, that the test fails, although it throws — as expected — an IllegalStateException. Do I have to configure something else to make …

Read More
How do you assert that a certain exception is thrown in JUnit 4 tests?

How can I use JUnit4 idiomatically to test that some code throws an exception? While I can certainly do something like this: @Test public void testFooThrowsIndexOutOfBoundsException() { boolean thrown = false; try { foo.doStuff(); } catch (IndexOutOfBoundsException e) { thrown = true; } assertTrue(thrown); } I …

Read More