What is the main difference between
@Before
and @BeforeClass
@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?
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'.