testing-pyramid

Testing Pyramid

Structure

Unit Tests         — fast, no Spring context, mock dependencies    (70%)
Slice Tests        — partial Spring context (@WebMvcTest, @DataJpaTest) (20%)
Integration Tests  — full context + real DB via Testcontainers     (10%)

Unit Tests — Services

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {

    @Mock private OrderRepository orderRepository;
    @Mock private InventoryService inventoryService;

    @InjectMocks private OrderService orderService;

    @Test
    void createOrder_whenItemsAvailable_shouldSaveAndReturnOrder() {
        // Given
        var request = new CreateOrderRequest("[email protected]", List.of(new OrderItemRequest(UUID.randomUUID(), 2)));
        var savedOrder = Order.create("[email protected]");
        when(orderRepository.save(any(Order.class))).thenReturn(savedOrder);
        doNothing().when(inventoryService).reserve(any());

        // When
        Order result = orderService.createOrder(request);

        // Then
        assertThat(result).isNotNull();
        assertThat(result.getCustomerEmail()).isEqualTo("[email protected]");
        verify(inventoryService).reserve(request.items());
        verify(orderRepository).save(any(Order.class));
    }

    @Test
    void createOrder_whenInventoryUnavailable_shouldThrowException() {
        // Given
        var request = new CreateOrderRequest("[email protected]", List.of());
        doThrow(new InsufficientInventoryException("Out of stock"))
            .when(inventoryService).reserve(any());

        // When / Then
        assertThatThrownBy(() -> orderService.createOrder(request))
            .isInstanceOf(InsufficientInventoryException.class)
            .hasMessage("Out of stock");
    }
}

Slice Tests — Controllers (@WebMvcTest)

// POSTs need .with(csrf()): @WebMvcTest applies Boot's default security (CSRF on);
// @WithMockUser only authenticates. Add @Import(SecurityConfig.class) to test your real rules.
// import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.csrf;
@WebMvcTest(OrderController.class)
class OrderControllerTest {

    @Autowired MockMvc mockMvc;
    @Autowired ObjectMapper objectMapper;
    @MockitoBean OrderService orderService; // Spring Boot 3.4+: @MockBean is deprecated

    @Test
    @WithMockUser(roles = "USER")
    void createOrder_withValidRequest_shouldReturn201() throws Exception {
        // Given
        var request = new CreateOrderRequest("[email protected]",
            List.of(new OrderItemRequest(UUID.randomUUID(), 1))); // items are @NotEmpty
        var order = Order.create("[email protected]");
        when(orderService.createOrder(any())).thenReturn(order);

        // When / Then
        mockMvc.perform(post("/api/v1/orders").with(csrf())
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(request)))
            .andExpect(status().isCreated())
            .andExpect(jsonPath("$.success").value(true))
            .andExpect(jsonPath("$.data.customerEmail").value("[email protected]"));
    }

    @Test
    @WithMockUser
    void createOrder_withInvalidRequest_shouldReturn400() throws Exception {
        mockMvc.perform(post("/api/v1/orders").with(csrf())
                .contentType(MediaType.APPLICATION_JSON)
                .content("{}")) // missing required fields
            .andExpect(status().isBadRequest())
            .andExpect(jsonPath("$.success").value(false))
            .andExpect(jsonPath("$.error.code").value("VALIDATION_FAILED"));
    }
}