What steps should I take to migrate from JUnit 4 to JUnit 5 with Mockito

Step 1: Update Dependencies

First, you need to update your project dependencies to include JUnit 5. JUnit 5 consists of three main modules: JUnit Jupiter, JUnit Platform, and JUnit Vintage. The JUnit Vintage module allows you to run JUnit 4 tests alongside JUnit 5 tests, making the migration process smoother[1][4].

For Maven, add the following dependencies to your `pom.xml`:

xml

    org.junit.jupiter
    junit-jupiter-api
    5.9.2
    test


    org.junit.jupiter
    junit-jupiter-engine
    5.9.2
    test


    org.junit.vintage
    junit-vintage-engine
    5.9.2
    test

For Gradle, add these to your `build.gradle`:

groovy
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.9.2'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.9.2'
testRuntimeOnly 'org.junit.vintage:junit-vintage-engine:5.9.2'

Step 2: Replace JUnit 4 Annotations

JUnit 5 introduces new annotations that replace or modify the behavior of JUnit 4 annotations. Here are some key replacements:

- `@Test`: Remains the same.
- `@Before` and `@After`: Replaced by `@BeforeEach` and `@AfterEach`.
- `@BeforeClass` and `@AfterClass`: Replaced by `@BeforeAll` and `@AfterAll`.
- `@Ignore`: Replaced by `@Disabled`.

Step 3: Integrate Mockito with JUnit 5

To use Mockito with JUnit 5, you need to add the Mockito JUnit Jupiter extension. This allows you to use Mockito annotations like `@Mock` without manually initializing them.

Add the following dependency to your project:

For Maven:

xml

    org.mockito
    mockito-junit-jupiter
    4.1.0
    test

For Gradle:

groovy
testImplementation 'org.mockito:mockito-core:4.1.0'
testImplementation 'org.mockito:mockito-junit-jupiter:4.1.0'

Then, annotate your test class with `@ExtendWith(MockitoExtension.class)` to enable Mockito's extension:

java
@ExtendWith(MockitoExtension.class)
public class MyTest {
    
    @Mock
    private MyService myService;
    
    @Test
    void testMyMethod() {
        // Use Mockito to mock behavior
        when(myService.doSomething()).thenReturn("Mocked Result");
        
        // Perform test logic
    }
}

Step 4: Replace Runners and Rules

JUnit 5 uses an extension model instead of runners and rules. This means you need to adapt any custom runners or rules to extensions. For example, if you were using `@RunWith(MockitoJUnitRunner.class)` in JUnit 4, you would use `@ExtendWith(MockitoExtension.class)` in JUnit 5[1][5].

Step 5: Test and Refactor

After making these changes, run your tests to ensure everything works as expected. You might need to refactor some tests to take advantage of JUnit 5's features or to fix any issues that arise during the migration.

Step 6: Remove JUnit 4 Dependencies

Once all tests are migrated and working, you can safely remove the JUnit 4 dependencies from your project[4][9].

By following these steps, you can smoothly migrate your tests from JUnit 4 to JUnit 5 while integrating Mockito for mocking dependencies.