JUnit 5 Extension

JUnit 5 Extensions are a powerful feature that allows you to extend the behavior of JUnit 5 tests. Extensions can be used to add new functionality to your tests, such as custom reporting, data injection, or mocking.

In this blog post, we will explore how to use JUnit 5 Extensions and provide some examples of how they can be used.

Creating a JUnit 5 Extension

Creating a JUnit 5 Extension is very simple. You simply need to create a class that implements the Extension interface. The Extension interface has no methods, so you do not need to implement any methods.

  
public class MyExtension implements Extension {
// Extension code goes here
}

Using a JUnit 5 Extension

Once you have created your JUnit 5 Extension, you can use it in your test class by annotating your test class or test method with the @ExtendWith annotation.

  
@ExtendWith(MyExtension.class)
public class MyTestClass {
// Test methods go here
}

If you want to apply an extension to a specific test method, you can annotate the method with the @ExtendWith annotation.

  
public class MyTestClass {
@Test
@ExtendWith(MyExtension.class)
public void myTest() {
// Test code goes here
}
}

JUnit 5 provides several built-in extensions that can be used out of the box. Here are a few examples:

ParameterResolver

The ParameterResolver extension allows you to inject parameters into your test methods. This is useful when you want to use the same object in multiple tests.

  
public class MyTestClass {
@Test
void myTest(@MyParameter MyObject myObject) {
// Test code goes here
}
}

  
public class MyParameterResolver implements ParameterResolver {
@Override
public boolean supportsParameter(ParameterContext parameterContext, ExtensionContext extensionContext) throws ParameterResolutionException {
return parameterContext.getParameter().getType() == MyObject.class;
}

    @Override
    public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) throws ParameterResolutionException {
        return new MyObject();
    }
}

TestWatcher

The TestWatcher extension allows you to add custom behavior before or after each test method. This is useful when you want to add custom reporting or logging.

  
public class MyTestWatcher extends TestWatcher {
@Override
protected void succeeded(ExtensionContext context) {
System.out.println("Test succeeded: " + context.getDisplayName());
}

    @Override
    protected void failed(Throwable e, ExtensionContext context) {
        System.out.println("Test failed: " + context.getDisplayName());
    }
}

  
@ExtendWith(MyTestWatcher.class)
public class MyTestClass {
@Test
void myTest() {
// Test code goes here
}
}

MockMvcExtension

The MockMvcExtension extension allows you to use the Spring MVC Test framework with JUnit 5 tests. This is useful when you want to test your Spring MVC controllers.

  
@ExtendWith(MockMvcExtension.class)
@WebMvcTest(MyController.class)
public class MyControllerTest {
@Autowired
private MockMvc mockMvc;

    @Test
    void myTest() throws Exception {
        mockMvc.perform(get("/myendpoint"))
               .andExpect(status().isOk());
    }
}

Conclusion

JUnit 5 Extensions are a powerful feature that allows you to extend the behavior of JUnit 5 tests. By creating your own extensions or using the built-in extensions, you can add new functionality to your tests, such as custom reporting, data injection, or mocking. By using JUnit 5 Extensions, you can write more

JUnit 5 Extension