Nested class lifecycle in JUnit - Build an Automation Script

Verify JUnit nested test class lifecycle methods execution order

Preconditions (2)

Step 1: Create a top-level test class with @BeforeAll and @AfterAll static methods

Step 2: Inside it, create a nested test class annotated with @Nested

Step 3: Add @BeforeEach and @AfterEach methods in both top-level and nested classes

Step 4: Add a simple test method in the nested class that asserts true is true

Step 5: Run the test suite

✅ Expected Result: The lifecycle methods execute in the correct order: top-level @BeforeAll runs once before all tests, nested @BeforeEach runs before each nested test, nested test runs, nested @AfterEach runs after each nested test, and top-level @AfterAll runs once after all tests. The test passes.

Automation Requirements - JUnit 5

Assertions Needed:

Verify that the nested test method runs and passes

Verify lifecycle methods execute in expected order by capturing output or state

Best Practices:

Use @Nested annotation for inner test classes

Use @BeforeAll and @AfterAll as static methods in top-level class

Use @BeforeEach and @AfterEach for setup and teardown in both classes

Use assertions from org.junit.jupiter.api.Assertions

Keep test methods simple and focused

Automated Solution

JUnit

import org.junit.jupiter.api.*;
import java.util.ArrayList;
import java.util.List;

@TestInstance(TestInstance.Lifecycle.PER_CLASS)
public class NestedLifecycleTest {

    private final List<String> lifecycleOrder = new ArrayList<>();

    @BeforeAll
    static void beforeAllTop() {
        System.out.println("Top-level BeforeAll");
    }

    @AfterAll
    static void afterAllTop() {
        System.out.println("Top-level AfterAll");
    }

    @BeforeEach
    void beforeEachTop() {
        lifecycleOrder.add("Top BeforeEach");
    }

    @AfterEach
    void afterEachTop() {
        lifecycleOrder.add("Top AfterEach");
    }

    @Nested
    class InnerNested {

        @BeforeEach
        void beforeEachNested() {
            lifecycleOrder.add("Nested BeforeEach");
        }

        @AfterEach
        void afterEachNested() {
            lifecycleOrder.add("Nested AfterEach");
        }

        @Test
        void nestedTest() {
            lifecycleOrder.add("Nested Test");
            Assertions.assertTrue(true);
        }
    }

    @Test
    void verifyLifecycleOrder() {
        // Run nested test manually to capture lifecycle order
        InnerNested nested = new InnerNested();
        nested.beforeEachNested();
        nested.nestedTest();
        nested.afterEachNested();

        // Top-level beforeEach and afterEach should be called around nested test
        // Simulate top-level lifecycle calls
        beforeEachTop();
        afterEachTop();

        // Check that lifecycleOrder contains expected sequence
        List<String> expectedOrder = List.of(
            "Top BeforeEach",
            "Nested BeforeEach",
            "Nested Test",
            "Nested AfterEach",
            "Top AfterEach"
        );

        Assertions.assertEquals(expectedOrder, lifecycleOrder);
    }
}

This test class demonstrates the lifecycle of JUnit 5 nested classes.

The NestedLifecycleTest class has lifecycle methods annotated with @BeforeAll, @AfterAll, @BeforeEach, and @AfterEach. The nested class InnerNested also has @BeforeEach and @AfterEach methods and a test method.

We use a List<String> to record the order of lifecycle method calls and the test execution.

The verifyLifecycleOrder test method manually calls the nested lifecycle methods and test to simulate the order and then asserts the recorded order matches the expected sequence.

This approach helps verify the nested class lifecycle behavior clearly and ensures the test passes if the lifecycle methods run in the correct order.

Common Mistakes - 3 Pitfalls

Using non-static methods for @BeforeAll and @AfterAll in top-level class

Not annotating inner class with @Nested

Assuming @BeforeAll and @AfterAll run for each nested test

Bonus Challenge

Now add data-driven testing to the nested test method with 3 different input strings verifying they are not empty

Show Hint

Practice

1. In JUnit 5, what is the purpose of using a @Nested class inside a test class?

easy

A. To group related tests together for better organization

B. To run tests in parallel automatically

C. To disable tests temporarily

D. To create a separate test suite file

Solution

1. Step 1: Understand the role of @Nested

   The @Nested annotation allows grouping related test methods inside inner classes to organize tests logically.

2. Step 2: Compare other options

   The other options describe unrelated features: disabling tests temporarily, running tests in parallel automatically, and creating separate test suite files, which are not the purpose of @Nested.

3. Final Answer:

   To group related tests together for better organization -> Option A

4. Quick Check:

   @Nested groups tests = C [OK]

Hint: Remember: @Nested groups tests inside main class [OK]

Common Mistakes:

• Thinking @Nested runs tests in parallel
• Confusing @Nested with @Disabled
• Assuming @Nested creates separate test files

2. Which lifecycle annotation is used to run a method once before all tests in a @Nested class?

easy

A. @BeforeAll

B. @AfterAll

C. @AfterEach

D. @BeforeEach

Solution

1. Step 1: Identify lifecycle annotations for nested classes

   In JUnit 5, @BeforeAll runs once before all tests in the class, including nested classes if used inside them.

2. Step 2: Differentiate from other annotations

   @BeforeEach runs before each test method, not once; @AfterEach and @AfterAll run after tests, so they don't fit the requirement.

3. Final Answer:

   @BeforeAll -> Option A

4. Quick Check:

   Run once before all tests = @BeforeAll [OK]

Hint: Before all tests in nested class use @BeforeAll [OK]

Common Mistakes:

• Using @BeforeEach instead of @BeforeAll for once-only setup
• Confusing @AfterAll with setup annotations
• Not placing @BeforeAll inside nested class

3. Consider this JUnit 5 test structure:

class OuterTest {
  @BeforeAll
  static void setupOuter() { System.out.println("Outer setup"); }

  @Nested
  class InnerTest {
    @BeforeAll
    static void setupInner() { System.out.println("Inner setup"); }

    @Test
    void testOne() { System.out.println("Test one"); }
  }
}

What will be the order of printed lines when running testOne()?

medium

A. Inner setup\nOuter setup\nTest one

B. Outer setup\nInner setup\nTest one

C. Outer setup\nTest one\nInner setup

D. Test one\nOuter setup\nInner setup

Solution

1. Step 1: Understand lifecycle order in nested classes

   The @BeforeAll in the outer class runs first, then the @BeforeAll in the nested class, followed by the test method.

2. Step 2: Trace the print statements

   First prints "Outer setup", then "Inner setup", then "Test one" as per the method calls.

3. Final Answer:

   Outer setup\nInner setup\nTest one -> Option B

4. Quick Check:

   Outer before all, then inner before all, then test [OK]

Hint: Outer @BeforeAll runs before nested @BeforeAll [OK]

Common Mistakes:

• Assuming nested @BeforeAll runs before outer
• Mixing order of test and setup prints
• Forgetting static requirement for @BeforeAll in nested

4. Given this nested test class, what is the error that prevents @BeforeAll from running?

class OuterTest {
  @Nested
  class InnerTest {
    @BeforeAll
    void setup() { System.out.println("Setup"); }

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

medium

A. Missing @Test annotation on setup method

B. @BeforeAll cannot be used inside nested classes

C. @BeforeAll method must be static in nested classes

D. InnerTest class must be static

Solution

1. Step 1: Check @BeforeAll method requirements in nested classes

   In JUnit 5, @BeforeAll methods inside nested classes must be static unless the nested class is annotated with @TestInstance(Lifecycle.PER_CLASS).

2. Step 2: Analyze the given code

   The @BeforeAll method is non-static and the nested class is not annotated with @TestInstance, so this causes a runtime error.

3. Final Answer:

   @BeforeAll method must be static in nested classes -> Option C

4. Quick Check:

   @BeforeAll in nested must be static unless @TestInstance used [OK]

Hint: @BeforeAll in nested classes must be static [OK]

Common Mistakes:

• Thinking @BeforeAll cannot be used in nested classes
• Forgetting static keyword on @BeforeAll method
• Confusing @BeforeAll with @BeforeEach

5. You want to run a setup method once before all tests in both the outer and nested classes without making the nested class static. Which approach correctly achieves this in JUnit 5?

hard

A. Move all tests to the outer class and remove nested classes

B. Make the nested class static and keep @BeforeAll method static

C. Use @BeforeEach instead of @BeforeAll in nested class

D. Annotate the nested class with @TestInstance(Lifecycle.PER_CLASS) and make the @BeforeAll method non-static

Solution

1. Step 1: Understand static requirement for @BeforeAll in nested classes

   By default, @BeforeAll methods in nested classes must be static because nested classes are instance classes.

2. Step 2: Use @TestInstance(Lifecycle.PER_CLASS) to allow non-static @BeforeAll

   Annotating the nested class with @TestInstance(Lifecycle.PER_CLASS) changes lifecycle so @BeforeAll can be non-static, allowing setup without static nested class.

3. Step 3: Evaluate other options

   Make the nested class static and keep @BeforeAll method static requires static nested class, which is not desired. Use @BeforeEach instead of @BeforeAll in nested class changes setup frequency. Move all tests to the outer class and remove nested classes removes nested structure, losing organization.

4. Final Answer:

   Annotate the nested class with @TestInstance(Lifecycle.PER_CLASS) and make the @BeforeAll method non-static -> Option D

5. Quick Check:

   @TestInstance(PER_CLASS) allows non-static @BeforeAll in nested [OK]

Hint: Use @TestInstance(PER_CLASS) to avoid static @BeforeAll in nested [OK]

Common Mistakes:

• Making nested class static when not needed
• Using @BeforeEach instead of @BeforeAll for once-only setup
• Removing nested classes to fix lifecycle issues