Introduction

Testing is a crucial part of software development, and Spring Boot provides a robust framework for testing your applications. This guide will delve into unit and integration testing in Spring Boot, complete with sample code and explanations.


Prerequisites

Before you start, make sure you have the following prerequisites:


Unit Testing

Unit tests focus on testing individual components, such as methods or classes, in isolation. Spring Boot provides tools for unit testing using libraries like JUnit. Here's an example unit test for a service class:

import org.junit.jupiter.api.Test;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
import static org.mockito.Mockito.*;
public class MyServiceUnitTest {
    @Mock
    private MyRepository myRepository;
    private MyService myService;
    @Test
    public void testServiceMethod() {
        MockitoAnnotations.initMocks(this);
        myService = new MyService(myRepository);
        when(myRepository.getData()).thenReturn("Mocked Data");
        String result = myService.doSomething();
        verify(myRepository).getData();
        assertEquals("Expected Result", result);
    }
}

In this example, we use the Mockito library to mock the repository and isolate the unit under test, the service method.


Integration Testing

Integration tests focus on testing interactions between components within the application. Spring Boot provides tools for integration testing using an embedded application context. Here's an example integration test for a controller:

import org.junit.jupiter.api.Test;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.beans.factory.annotation.Autowired;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
@SpringBootTest
@AutoConfigureMockMvc
public class MyControllerIntegrationTest {
    @Autowired
    private MockMvc mockMvc;
    @Test
    public void testControllerEndpoint() throws Exception {
        mockMvc.perform(get("/my-endpoint"))
            .andExpect(status().isOk());
    }
}

In this example, we use the Spring Boot testing annotations to load the application context and perform HTTP requests against a controller endpoint.


Conclusion

Testing in Spring Boot is essential to ensure the reliability and correctness of your applications. This guide covered unit testing using JUnit and Mockito, and integration testing with Spring Boot's testing tools. With these techniques, you can confidently test your Spring Boot applications.