Test

Spring Boot Testing Guide

Spring Boot provides various tools and annotations to help developers effectively test their applications. Testing can be divided into unit testing, integration testing, and end-to-end testing. This document outlines some commonly used testing annotations and features.

@SpringBootTest

• Purpose: Loads the entire Spring application context, suitable for integration testing.
• Functionality: Starts a complete Spring Boot application context, including all Beans and configurations.
• Example:

  @SpringBootTest
  public class MyServiceTest {

      @Autowired
      private MyService myService;

      @Test
      public void testService() {
          assertNotNull(myService);
      }
  }

@MockBean

•   Purpose: Creates mock objects in Spring Boot tests and injects them into the Spring container.
•   Functionality: Replaces Beans in the application context to simulate the behavior of dependencies.
•   Example:

    @SpringBootTest
    public class MyServiceTest {
        @MockBean
        private MyRepository myRepository;

        @Autowired
        private MyService myService;

        @Test
        public void testService() {
            when(myRepository.findById(1L)).thenReturn(Optional.of(new MyEntity()));
            assertNotNull(myService.getEntityById(1L));
        }
    }

@WebMvcTest

•   Purpose: Tests Spring MVC controllers, creating a minimal Spring context.
•   Functionality: Loads only the Web layer Beans, not the full application context.
•   Example:

    @WebMvcTest(MyController.class)
    public class MyControllerTest {

        @Autowired
        private MockMvc mockMvc;

        @Test
        public void testController() throws Exception {
            mockMvc.perform(get("/my-endpoint"))
                .andExpect(status().isOk())
                .andExpect(content().string("Hello, world!"));
        }
    }

@DataJpaTest

•   Purpose: Tests Spring Data JPA components, creating a context with only JPA-related Beans.
•   Functionality: Focuses on the data access layer, automatically configuring an embedded database.
•   Example:

        @DataJpaTest
        public class MyRepositoryTest {

            @Autowired
            private MyRepository myRepository;

            @Test
            public void testRepository() {
                MyEntity entity = new MyEntity();
                myRepository.save(entity);
                assertNotNull(myRepository.findById(entity.getId()));
            }
        }

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)

•   Purpose: Tests the entire Spring Boot application, including the Web layer, by starting an embedded web server with a random port.
•   Functionality: Suitable for integration tests that require real HTTP requests.
•   Example:

    @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
    public class MyApplicationTest {

        @LocalServerPort
        private int port;

        @Test
        public void testHttpEndpoint() throws Exception {
            URL url = new URL("http://localhost:" + port + "/my-endpoint");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            assertEquals(200, connection.getResponseCode());
        }
    }

Common Testing Tools and Methods

MockMvc

•   Purpose: Used to test Spring MVC controllers by simulating HTTP requests and responses to verify controller behavior.
•   Example:

    @Autowired
    private MockMvc mockMvc;

    @Test
    public void testController() throws Exception {
        mockMvc.perform(get("/endpoint"))
            .andExpect(status().isOk())
            .andExpect(content().string("Expected content"));
    }

TestRestTemplate

•   Purpose: Used to test RESTful APIs in Spring Boot applications, providing access to the embedded web server.
•   Example:

    @Autowired
    private TestRestTemplate restTemplate;

    @Test
    public void testRestApi() {
        ResponseEntity<String> response = restTemplate.getForEntity("/endpoint", String.class);
        assertEquals(HttpStatus.OK, response.getStatusCode());
        assertEquals("Expected content", response.getBody());
    }

@AutoConfigureMockMvc

•   Purpose: Configures and injects a MockMvc instance for Web layer testing.
•   Example:

    @AutoConfigureMockMvc
    @SpringBootTest
    public class MyControllerTest {

        @Autowired
        private MockMvc mockMvc;

        @Test
        public void testController() throws Exception {
            mockMvc.perform(get("/endpoint"))
                .andExpect(status().isOk())
                .andExpect(content().string("Expected content"));
        }
    }

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