Testing

Spring Boot bundles JUnit Jupiter, AssertJ, Mockito and Spring Test, and supports both slice tests, which start only part of the application, and integration tests, which start all of it. This chapter goes from the fastest kind of test to the slowest.

Test dependencies and running tests

Projects generated by Initializr include a test starter per technology (spring-boot-starter-webmvc-test, spring-boot-starter-data-jpa-test and so on). Run tests through the build tool:

./gradlew test
./mvnw test

# Run a single test class
./gradlew test --tests "com.example.demo.todo.TodoServiceTests"

Plain unit tests

With constructor injection you can create objects by hand and test them without Spring at all. These tests are the fastest, so use them for business rules.

class GreetingServiceTests {

    @Test
    void greetsInTheMorning() {
        Clock morning = Clock.fixed(Instant.parse("2025-01-01T08:00:00Z"), ZoneOffset.UTC);
        GreetingService service = new GreetingService(morning);

        assertThat(service.greet("Kim")).isEqualTo("Good morning, Kim");
    }
}

Web slice: @WebMvcTest

@WebMvcTest starts only the MVC infrastructure (controllers, JSON conversion, validation) and registers no services or repositories. Replace the beans a controller depends on with mocks via @MockitoBean. MockMvcTester lets you assert on requests and responses in AssertJ style.

@WebMvcTest(TodoController.class)
class TodoControllerTests {

    @Autowired
    MockMvcTester mvc;

    @MockitoBean
    TodoService service;

    @Test
    void returnsTodo() {
        given(service.find(1L)).willReturn(new TodoResponse(1L, "Write docs", false));

        assertThat(mvc.get().uri("/api/todos/1"))
            .hasStatusOk()
            .bodyJson().extractingPath("$.title").isEqualTo("Write docs");
    }

    @Test
    void rejectsBlankTitle() {
        assertThat(mvc.post().uri("/api/todos")
                .contentType(MediaType.APPLICATION_JSON)
                .content("{\"title\": \"\"}"))
            .hasStatus(HttpStatus.BAD_REQUEST);
    }
}

The previous generation used @MockBean; it has been replaced by Spring Framework's @MockitoBean.

Data slice: @DataJpaTest

@DataJpaTest configures only JPA-related beans and runs each test in a transaction that is rolled back afterwards. If an embedded database such as H2 is on the classpath, it is used in place of your configured one by default. To run the example below as is, add testRuntimeOnly("com.h2database:h2"), or use Testcontainers as shown later.

@DataJpaTest
class TodoRepositoryTests {

    @Autowired
    TestEntityManager entityManager;

    @Autowired
    TodoRepository repository;

    @Test
    void findsOpenTodos() {
        entityManager.persist(new Todo("open"));
        Todo done = new Todo("done");
        done.complete();
        entityManager.persist(done);

        assertThat(repository.findByDoneFalseOrderByIdAsc())
            .extracting(Todo::getTitle)
            .containsExactly("open");
    }
}