Test Spring MVC Controllers with MockMvc

MockMvc exercises Spring MVC request handling without starting a real HTTP server.

@WebMvcTest(UserController.class)
class UserControllerTest {
    @Autowired MockMvc mockMvc;

    @MockBean UserService userService;

    @Test
    void returnsUser() throws Exception {
        given(userService.findById(1L))
            .willReturn(new UserDto(1L, "Tom"));

        mockMvc.perform(get("/users/{id}", 1))
            .andExpect(status().isOk())
            .andExpect(content().contentTypeCompatibleWith("application/json"))
            .andExpect(jsonPath("$.id").value(1))
            .andExpect(jsonPath("$.name").value("Tom"));
    }
}

Use @WebMvcTest for a focused controller slice and mock service dependencies. Use @SpringBootTest with @AutoConfigureMockMvc when filters, serialization, validation, security, and broader configuration must be integrated.

Assert both success and failure contracts: invalid input, missing resources, authorization, content type, and exception-handler responses. Avoid assertions that depend on irrelevant JSON field order.