MockMvc

Test Spring MVC controllers with MockMvc — the fluent API for testing HTTP request handling, response status, JSON content, and security without starting a real server.

@WebMvcTest(ProductController.class)
class ProductControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private ProductService productService;

    @Autowired
    private ObjectMapper objectMapper;

    @Test
    @WithMockUser
    void getProducts_returnsPagedResults() throws Exception {
        Page<ProductDto> page = new PageImpl<>(
            List.of(new ProductDto(1L, "Laptop", BigDecimal.valueOf(999.99))),
            PageRequest.of(0, 20),
            1
        );
        when(productService.findAll(any(Pageable.class))).thenReturn(page);

        mockMvc.perform(get("/api/v1/products")
                .param("page", "0")
                .param("size", "20")
                .contentType(MediaType.APPLICATION_JSON))
            .andDo(print())  // helpful for debugging
            .andExpect(status().isOk())
            .andExpect(content().contentType(MediaType.APPLICATION_JSON))
            .andExpect(jsonPath("$.content").isArray())
            .andExpect(jsonPath("$.content[0].id").value(1))
            .andExpect(jsonPath("$.content[0].name").value("Laptop"))
            .andExpect(jsonPath("$.totalElements").value(1));
    }

    @Test
    @WithMockUser
    void createProduct_validRequest_returns201WithLocation() throws Exception {
        CreateProductRequest request = new CreateProductRequest(
            "Laptop Pro", BigDecimal.valueOf(1299.99), "ELECTRONICS");
        ProductDto created = new ProductDto(42L, "Laptop Pro", BigDecimal.valueOf(1299.99));
        when(productService.create(any())).thenReturn(created);

        mockMvc.perform(post("/api/v1/products")
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(request)))
            .andExpect(status().isCreated())
            .andExpect(header().string("Location", containsString("/api/v1/products/42")))
            .andExpect(jsonPath("$.id").value(42));
    }

    @Test
    @WithMockUser
    void createProduct_missingName_returns400WithValidationError() throws Exception {
        CreateProductRequest request = new CreateProductRequest(
            "", BigDecimal.valueOf(100), "ELECTRONICS"); // blank name

        mockMvc.perform(post("/api/v1/products")
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(request)))
            .andExpect(status().isBadRequest())
            .andExpect(jsonPath("$.errorCode").value("VALIDATION_FAILED"))
            .andExpect(jsonPath("$.fieldErrors[0].field").value("name"));
    }

    @Test
    void getProducts_unauthenticated_returns401() throws Exception {
        mockMvc.perform(get("/api/v1/products"))
            .andExpect(status().isUnauthorized());
    }

    @Test
    @WithMockUser(roles = "USER")  // Not ADMIN
    void deleteProduct_notAdmin_returns403() throws Exception {
        mockMvc.perform(delete("/api/v1/products/1"))
            .andExpect(status().isForbidden());
    }
}

MockMvc tests are the best ROI in your test suite. They test the full controller pipeline including validation, serialization, and error handling — without the overhead of a real server. Write MockMvc tests for every endpoint: happy path, validation failure, authentication failure, authorization failure, and not-found cases. These tests catch the most common API bugs.