SivaLabs

In the previous Getting Started with Spring Boot tutorial, we have learned how to create a Spring Boot application and built a simple REST API.

In this tutorial, you will learn how to write unit, slice and integration tests for your Spring Boot application.

Testing Spring Boot applications

We should write Unit Tests to verify the business logic of a particular unit(a class, a method, or a set of classes), and they shouldn’t be talking to any external services like database, queues or other webservices etc. If the unit we are testing depends on any of those external services, then we can provide mock implementations of those dependencies and verify the unit’s behaviour.

In addition to Unit Tests, we should write Integration Tests which exercise the behaviour of a sub-system or a component by talking to the real services and dependent collaborators.

When we generate our Spring Boot application spring-boot-starter-test dependency is automatically added which transitively adds the most commonly used testing libraries such as SpringTest, JUnit5, Mockito, Assertj, JsonPath, JsonAssert to our application as test dependencies.

Types of Tests

Unit Tests: These are the tests to verify the behaviour of a single unit, and ideally they shouldn’t depend on frameworks like Spring or Hibernate, etc.

Slice Tests: These are the tests to verify a slice of the application such as Web layer or Persistence layer etc. Spring Boot provides support for testing slices of the application using @WebMvcTest, @DataJpaTest, @DataMongoTest etc.

Integration Tests: These are the tests, which tests the application in a blackbox manner. We pass in some input, and we expect specific output, we don’t know or care how it works internally. Spring Boot provides support for writing Integration Tests using @SpringBootTest.

Unit Testing with JUnit 5 and Mockito

We are going to write tests for the REST API we have implemented in the previous Getting Started with Spring Boot tutorial.

Let’s start with writing Unit Tests for GreetingService. We will use JUnit 5 and Mockito for writing unit tests.

src/test/java/com/sivalabs/helloworld/GreetingServiceTest.java

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.BDDMockito.given;

@ExtendWith(MockitoExtension.class) // (1)
class GreetingServiceTest {

    @Mock // (2)
    private ApplicationProperties properties;

    @InjectMocks // (3)
    private GreetingService greetingService;

    @BeforeEach // (4)
    void setUp() {
        given(properties.getGreeting()).willReturn("Hello");
    }

    @Test
    void shouldGreetWithDefaultNameWhenNameIsNotProvided() {
        given(properties.getDefaultName()).willReturn("World");

        String greeting = greetingService.sayHello(null);

        Assertions.assertEquals("Hello World", greeting); //JUnit 5 based assertion (5)
        assertThat(greeting).isEqualTo("Hello World"); //Assertj based assertion (6)
    }

    @Test
    void shouldGreetWithGivenName() {
        String greeting = greetingService.sayHello("John");

        assertThat(greeting).isEqualTo("Hello John");
    }
}

• (1) We are using MockitoExtension so that we can create mock objects and inject them using annotations.
• (2) The @Mock annotation will initialize properties with a mock implementation of ApplicationProperties class.
• (3) The @InjectMocks annotation will create an instance of GreetingService by injecting the dependencies (properties) using the defined mock objects.
• (4) The @BeforeEach annotated method will be executed before each test execution so that we can put any common test setup in there.
• (5) We are asserting the expected output with actual output using JUnit 5 based assertions.
• (6) We are asserting the expected output with actual output using Assertj based assertions.

Testing application slices using Spring’s Test Slice annotations

Now let’s write a test for HelloWorldController using @WebMvcTest.

With @WebMvcTest only the web layer components such as Controllers, Interceptors, etc will be loaded into ApplicationContext. So we need to add dependent beans by some means such as using @MockBean or configuring dependent beans using @TestConfiguration.

In our unit test we used Mockito’s @Mock annotation to create a mock bean, but here we are using Spring’s @MockBean instead of @Mock. While using @WebMvcTest the test instance and ApplicationContext creation is taken care by Spring, which is unaware of plain mock objects created by @Mock. When you use Spring’s @MockBean that mock bean will become part of ApplicationContext and will be injected into the Controller.

src/test/java/com/sivalabs/helloworld/HelloWorldControllerTest.java

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.test.web.servlet.MockMvc;

import static org.hamcrest.CoreMatchers.is;
import static org.mockito.BDDMockito.given;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@WebMvcTest(controllers = HelloWorldController.class) // (1)
class HelloWorldControllerTest {
    @Autowired
    private MockMvc mockMvc; // (2)

    @MockBean
    private GreetingService greetingService; // (3)

    @Test
    void shouldReturnGreetingSuccessfully() throws Exception {
        given(greetingService.sayHello("Siva")).willReturn("Hello Siva"); // (4)

        mockMvc.perform(get("/api/hello?name={name}", "Siva"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.greeting", is("Hello Siva"))); // (5)
    }
}

• (1) Using @WebMvcTest(controllers = HelloWorldController.class) we are only testing the web layer controller and loading only HelloWorldController.
• (2) While using @WebMvcTest annotation MockMvc will be autoconfigured, and we can autowire and use it to invoke API endpoints.
• (3) Using @MockBean we are injecting a mock GreetingService bean into HelloWorldController.
• (4) Setting up the mock behaviour on mock GreetingService bean.
• (5) Invoking GET /api/hello API and asserting the Http Response Code and body using jsonPath assertions.

Integration Tests using @SpringBootTest

Finally, let’s write an integration test which loads the entire application then make an API call and test the results.

src/test/java/com/sivalabs/helloworld/SpringBootHelloWorldApplicationTests.java

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.servlet.MockMvc;

import static org.hamcrest.CoreMatchers.is;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@SpringBootTest(webEnvironment= SpringBootTest.WebEnvironment.RANDOM_PORT) // (1)
@AutoConfigureMockMvc  // (2)
class SpringBootHelloWorldApplicationTests {

    @Autowired
    private MockMvc mockMvc;

    @Test
    void shouldReturnGreetingSuccessfully() throws Exception {
        mockMvc.perform(get("/api/hello?name={name}", "Siva"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.greeting", is("Hello Siva")));
    }
}

• (1) We are using @SpringBootTest to load the entire application and also specified webEnvironment= SpringBootTest.WebEnvironment.RANDOM_PORT to start the application on a random available port so that there won’t be any port conflicts with any running applications. This is especially very useful while running tests on build servers like Jenkins where multiple application builds run in parallel.
• (2) While using @SpringBootTest the MockMvc bean won’t be autoconfigured, so we are using @AutoConfigureMockMvc to configure the MockMvc bean.

Run tests

We can run tests using the build tool as follows:

Maven:

./mvnw verify

Gradle:

./gradlew test

Summary

We have learned how to write unit tests using JUnit 5 and Mockito. Then we learned about testing a slice of the application using Spring Boot Test Slice support. Finally, we have learned how to write an integration test by bootstrapping the entire application.