How to Use JUnit with Spring Boot for Testing

To use JUnit with Spring Boot, add the spring-boot-starter-test dependency which includes JUnit 5. Annotate your test classes with @SpringBootTest to load the application context and write test methods with @Test to verify your code.

Syntax

Use @SpringBootTest on your test class to start the Spring Boot context. Use @Test to mark test methods. Inject beans with @Autowired to test Spring components.

• @SpringBootTest: Loads full application context.
• @Test: Marks a method as a test.
• @Autowired: Injects Spring beans into tests.

java

import org.springframework.boot.test.context.SpringBootTest;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;

@SpringBootTest
public class MyServiceTest {

    @Autowired
    private MyService myService;

    @Test
    void testServiceMethod() {
        // test logic here
    }
}

Example

This example shows a simple Spring Boot test class that checks if a service method returns the expected result.

java

import org.springframework.boot.test.context.SpringBootTest;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import static org.junit.jupiter.api.Assertions.assertEquals;

@SpringBootTest
public class CalculatorServiceTest {

    @Autowired
    private CalculatorService calculatorService;

    @Test
    void testAdd() {
        int result = calculatorService.add(2, 3);
        assertEquals(5, result, "2 + 3 should equal 5");
    }
}

// Service class
import org.springframework.stereotype.Service;

@Service
public class CalculatorService {
    public int add(int a, int b) {
        return a + b;
    }
}

Output

Test passed: testAdd()

Common Pitfalls

• Not including spring-boot-starter-test dependency causes missing JUnit classes.
• Forgetting @SpringBootTest means Spring context won’t load, causing NullPointerException on autowired beans.
• Using JUnit 4 annotations (@RunWith) instead of JUnit 5 (@ExtendWith) in new Spring Boot versions.
• Writing tests without assertions leads to tests that always pass.

java

/* Wrong: Missing @SpringBootTest causes null bean */

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;

public class WrongTest {

    @Autowired
    private CalculatorService calculatorService; // will be null

    @Test
    void testAdd() {
        // NullPointerException here
        int result = calculatorService.add(1, 1);
    }
}

/* Right: Add @SpringBootTest to load context */

import org.springframework.boot.test.context.SpringBootTest;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import static org.junit.jupiter.api.Assertions.assertEquals;

@SpringBootTest
public class RightTest {

    @Autowired
    private CalculatorService calculatorService;

    @Test
    void testAdd() {
        int result = calculatorService.add(1, 1);
        assertEquals(2, result);
    }
}

Quick Reference

Remember these key points when using JUnit with Spring Boot:

• Add spring-boot-starter-test dependency.
• Use @SpringBootTest to load Spring context.
• Write test methods with @Test and include assertions.
• Inject beans with @Autowired for integration tests.
• Use JUnit 5 annotations and features.

Key Takeaways

Add spring-boot-starter-test dependency to include JUnit and Spring test tools.

Annotate test classes with @SpringBootTest to load the full Spring Boot context.

Use @Test to mark test methods and include assertions to verify behavior.

Inject Spring beans in tests with @Autowired for integration testing.

Avoid mixing JUnit 4 and JUnit 5 annotations; prefer JUnit 5 in modern Spring Boot.