JUnit 5 Test Lifecycle | Java Fresher Interview

Direct Answer

For a simple Jupiter test class, @BeforeAll runs before its test invocations, then each invocation is surrounded by @BeforeEach and @AfterEach, and @AfterAll runs at the end. The default PER_METHOD lifecycle creates a new test instance for each test method or invocation. That isolates ordinary instance fields, but static fields, external systems, and other shared state can still couple tests.

Deep Dive & Architecture

JUnit begins the class lifecycle with @BeforeAll and ends it with @AfterAll. Between those hooks, every test invocation has its own cycle: JUnit creates the test instance under the default PER_METHOD mode, runs @BeforeEach, runs the test, and then runs @AfterEach.

For example, a class with two @Test methods runs the before-each and after-each hooks twice, but the before-all and after-all hooks once. The fresh instance prevents ordinary instance fields from leaking state between tests. Class-level lifecycle methods are therefore static by default. @TestInstance(PER_CLASS) permits non-static class-level hooks, but it also reuses one instance, so mutable fields must be reset deliberately. Test correctness must never depend on method order.

Code Example

class LifecycleTest {
    @BeforeAll  static void beforeAll()  { System.out.println("beforeAll"); }
    @BeforeEach void beforeEach()        { System.out.println("  beforeEach"); }
    @Test       void testOne()           { System.out.println("    testOne"); }
    @Test       void testTwo()           { System.out.println("    testTwo"); }
    @AfterEach  void afterEach()         { System.out.println("  afterEach"); }
    @AfterAll   static void afterAll()   { System.out.println("afterAll"); }
}
// beforeAll appears first and afterAll last. Each test name is surrounded
// by beforeEach and afterEach. testOne and testTwo may run in either order
// unless a method orderer is configured.

Common Mistakes & Pitfalls

• Assuming one shared instance. Under the default lifecycle each test method or invocation gets a new instance; static fields and external systems can still carry state.
• @BeforeAll before each test. It runs once for the container, not per invocation — that is @BeforeEach.
• Non-static @BeforeAll under PER_METHOD. Jupiter rejects the lifecycle method unless it is static; PER_CLASS permits an instance method.
• Relying on source order. Test order is controlled only when an explicit orderer is configured, and ordinary tests should not depend on one another.