Mockito verify()

Introduction

The verify() method in Mockito is used to check if certain methods on mock objects were called with specific arguments. This is particularly useful for verifying interactions and ensuring that the code under test is correctly interacting with its dependencies. This tutorial will demonstrate how to use the verify() method in Mockito to check method invocations.

Maven Dependencies

To use Mockito with JUnit 5, add the following dependencies to your pom.xml file:

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-core</artifactId>
    <version>4.8.1</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-junit-jupiter</artifactId>
    <version>4.8.1</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-engine</artifactId>
    <version>5.9.2</version>
    <scope>test</scope>
</dependency>

Example Scenario

We will create a UserService class that has a dependency on a UserRepository. Our goal is to test the UserService methods using the verify() method in Mockito to check if the interactions with the UserRepository are as expected.

UserService and UserRepository Classes

First, create the User class, the UserRepository interface, and the UserService class.

public class User {
    private String name;
    private String email;

    // Constructor, getters, and setters
    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

public interface UserRepository {
    void saveUser(User user);
    User findUserByEmail(String email);
}

public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public void registerUser(String name, String email) {
        User user = new User(name, email);
        userRepository.saveUser(user);
    }

    public User getUserByEmail(String email) {
        return userRepository.findUserByEmail(email);
    }
}

JUnit 5 Test Class with Mockito

Create a test class for UserService using JUnit 5 and Mockito.

import static org.mockito.Mockito.*;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import org.junit.jupiter.api.extension.ExtendWith;

@ExtendWith(MockitoExtension.class)
public class UserServiceTest {

    @Mock
    private UserRepository userRepository;

    @InjectMocks
    private UserService userService;

    @Test
    public void testRegisterUser() {
        // Given
        String name = "John Doe";
        String email = "john.doe@example.com";

        // When
        userService.registerUser(name, email);

        // Then
        verify(userRepository).saveUser(new User(name, email));
    }

    @Test
    public void testGetUserByEmail() {
        // Given
        String email = "jane.doe@example.com";
        User user = new User("Jane Doe", email);
        when(userRepository.findUserByEmail(email)).thenReturn(user);

        // When
        User result = userService.getUserByEmail(email);

        // Then
        assertNotNull(result);
        assertEquals("Jane Doe", result.getName());
        assertEquals(email, result.getEmail());
        verify(userRepository).findUserByEmail(email);
    }
}

Explanation

1. The @Mock annotation creates a mock instance of the UserRepository interface. This mock instance can be used to simulate the behavior of the UserRepository in a controlled way.
2. The @InjectMocks annotation injects the mock UserRepository into the UserService instance to provide a controlled test environment. This allows the UserService methods to be tested in isolation from the actual UserRepository implementation.
3. The verify(userRepository).saveUser(new User(name, email)); method checks if the saveUser method was called on the UserRepository with the expected User object. This ensures that the registerUser method of the UserService class interacts with the UserRepository correctly.
4. The verify(userRepository).findUserByEmail(email); method checks if the findUserByEmail method was called on the UserRepository with the expected email. This ensures that the getUserByEmail method of the UserService class interacts with the UserRepository correctly.

Additional Scenarios

Scenario: Verifying Method Call Count

In this scenario, we will demonstrate how to verify the number of times a method was called using the verify() method.

@Test
public void testRegisterUserCalledOnce() {
    // Given
    String name = "John Doe";
    String email = "john.doe@example.com";

    // When
    userService.registerUser(name, email);

    // Then
    verify(userRepository, times(1)).saveUser(new User(name, email));
}

Scenario: Verifying No Interactions

In this scenario, we will demonstrate how to verify that no interactions occurred with the mock object using the verifyNoInteractions() method.

@Test
public void testNoInteractionsWithRepository() {
    // Given
    // No interactions expected

    // When
    // No method calls

    // Then
    verifyNoInteractions(userRepository);
}

Conclusion

The verify() method in Mockito simplifies the verification of method calls on mock objects for unit testing. By using verify(), you can easily check if certain methods were called with specific arguments, ensuring that the code under test interacts with its dependencies as expected. This step-by-step guide demonstrated how to effectively use the verify() method in your unit tests, covering different scenarios to ensure comprehensive testing of the UserService class.

Related Mockito Methods

Mockito mock()
Mockito spy()
Mockito when()
Mockito thenThrow()
Mockito verify()
Mockito times()
Mockito never()
Mockito any()
Mockito eq()
Mockito inOrder()
Mockito doReturn()
Mockito doThrow()
Mockito doAnswer()
Mockito timeout()
Mockito ArgumentMatchers