Why lifecycle hooks manage setup and teardown in JUnit - Test Execution Impact

Test Overview

This test demonstrates how JUnit lifecycle hooks @BeforeEach and @AfterEach manage setup and teardown for each test method. It verifies that setup runs before and teardown runs after the test.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.api.*;
import static org.junit.jupiter.api.Assertions.*;

public class LifecycleHooksTest {

    private StringBuilder resource;

    @BeforeEach
    void setUp() {
        resource = new StringBuilder("start");
    }

    @AfterEach
    void tearDown() {
        resource = null;
    }

    @Test
    void testModifyResource() {
        resource.append("-modified");
        assertEquals("start-modified", resource.toString());
    }

    @Test
    void testResourceIsFresh() {
        assertEquals("start", resource.toString());
    }
}

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and prepares to run testModifyResource	No resource initialized yet	-	PASS
2	@BeforeEach setUp() runs, initializing resource with 'start'	resource = 'start'	-	PASS
3	testModifyResource() runs, appending '-modified' to resource	resource = 'start-modified'	assertEquals("start-modified", resource.toString())	PASS
4	@AfterEach tearDown() runs, setting resource to null	resource = null	-	PASS
5	Test runner prepares to run testResourceIsFresh	resource is null from previous teardown	-	PASS
6	@BeforeEach setUp() runs again, initializing resource with 'start'	resource = 'start'	-	PASS
7	testResourceIsFresh() runs, checking resource value	resource = 'start'	assertEquals("start", resource.toString())	PASS
8	@AfterEach tearDown() runs, setting resource to null	resource = null	-	PASS

Failure Scenario

Failing Condition: If @BeforeEach setUp() does not initialize resource, tests fail due to NullPointerException or wrong value

Execution Trace Quiz - 3 Questions

What does the @BeforeEach method do in this test?

A Runs only once before all tests

B Cleans up the resource after all tests finish

C Initializes the resource before each test method runs

D Runs after each test method to reset the resource

Key Result

Using lifecycle hooks like @BeforeEach and @AfterEach ensures each test starts fresh and cleans up after itself, preventing tests from affecting each other.