How to Create a Java Test for a Spring Exception Handler

What is the best way to test an Exception Handler in a Spring application using Java?

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<String> handleResourceNotFound(ResourceNotFoundException ex) {
        return new ResponseEntity<>(ex.getMessage(), HttpStatus.NOT_FOUND);
    }
}

Testing an Exception Handler in a Spring application ensures that errors are managed correctly and responses are appropriate. This involves unit testing the handler to verify that it returns correct responses for specific exceptions.

@SpringBootTest
public class GlobalExceptionHandlerTest {

    @Autowired
    private MockMvc mockMvc;

    @Test
    public void testHandleResourceNotFound() throws Exception {
        mockMvc.perform(get("/api/resource/1"))
               .andExpect(status().isNotFound())
               .andExpect(content().string("Resource not found"));
    }
}

Causes

• Failure to return the right HTTP status code on exception.
• Incorrect handling of exception messages in responses.
• Not validating that exceptions are caught properly.

Solutions

• Use MockMvc to simulate requests and responses.
• Ensure you're testing the correct status codes are returned.
• Create various test cases for different exception scenarios.

Mistake: Not using MockMvc to precisely emulate HTTP requests.

Solution: Ensure proper setup of MockMvc to test controller and exception responses.

Mistake: Forgetting to assert the expected error response's content.

Solution: Always validate both HTTP status code and response body in your tests.