What can we test and verify with MockMvc?

That’s easy to answer: Everything related to Spring MVC!

This includes your controller endpoints (both @Controller and @RestController) and any Spring MVC infrastructure components like Filter, @ControllerAdvice, WebMvcConfigurer, etc.

Possible test scenarios can be the following:

• Does my REST API controller return a proper JSON response?
• Is the model for my Thymeleaf view properly initialized?
• Does my endpoint return the HTTP status code 418 if my service layer throws a TeaNotFoundException?
• Is my REST API endpoint properly protected with Basic Auth?
• Can only users with the role ADMIN access the DELETE endpoint?
• etc.

With MockMvc we perform requests against a mocked servlet environment. There won’t be any real HTTP communication during our tests. We rather directly work with the mocked environment provided by Spring.  MockMvc acts as the entry-point to this mocked servlet environment. Similar to the WebTestClient when accessing our started Servlet container over HTTP.