311-frameworks-spring-boot-slice-testing

Spring Boot Slice Testing

Spring Boot slice testing allows you to test specific layers or "slices" of your application in isolation, providing faster and more focused tests than full integration tests. This approach helps maintain test clarity, reduces test execution time, and improves maintainability.

Implementing These Principles

These guidelines are built upon the following core principles:

• Layer Isolation: Test each application layer independently without loading the entire Spring context
• Focused Testing: Use appropriate slice annotations to load only the components needed for specific functionality
• Mock Dependencies: Mock external dependencies and other layers to achieve true unit testing at the slice level
• Fast Execution: Minimize Spring context loading to achieve rapid test feedback cycles

Table of contents

• Rule 1: Use @WebMvcTest for Web Layer Testing
• Rule 2: Use @JdbcTest for Repository Layer Testing
• Rule 3: Use @JsonTest for JSON Serialization Testing
• Rule 4: Use @MockBean for Mocking Dependencies
• Rule 5: Configure Test Profiles Appropriately
• Rule 6: Use @TestConfiguration for Custom Test Setup

Rule 1: Use @WebMvcTest for Web Layer Testing

Title: Test Controllers in Isolation with @WebMvcTest Description: Use @WebMvcTest to test only the web layer (controllers) without loading the full application context. This annotation configures Spring MVC infrastructure and auto-configures MockMvc for testing HTTP requests and responses.

Good example:

@WebMvcTest(UserController.class)
class UserControllerTest {

    @Autowired
    private MockMvc mockMvc;
    
    @MockBean
    private UserService userService;
    
    @Test
    void shouldReturnUserWhenValidId() throws Exception {
        // Given
        User user = new User(1L, "John Doe", "[email protected]");
        when(userService.findById(1L)).thenReturn(user);
        
        // When & Then
        mockMvc.perform(get("/api/users/1"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.name").value("John Doe"))
            .andExpect(jsonPath("$.email").value("[email protected]"));
    }
}