Mockito BDDMockito then Method

The then method in the BDDMockito class is part of the Behavior-Driven Development (BDD) style of writing tests using Mockito. It is used to verify that a method on a mock object was called with specific arguments. This method is particularly useful for making tests more readable and aligning with the BDD style, which focuses on describing the behavior of the application in a clear and human-readable format.

Table of Contents

1. Introduction
2. then Method Syntax
3. Examples
   • Basic Usage
   • Using then with Argument Matchers
   • Using then with Verification Modes
4. Real-World Use Case
5. Conclusion

Introduction

Behavior-Driven Development (BDD) is a software development approach that emphasizes collaboration between developers, QA, and non-technical or business participants in a software project. Mockito’s BDDMockito class provides methods that support the BDD style of writing tests. The then method is used to verify that a method on a mock object was called with specific arguments, making tests more readable and intuitive.

then Method Syntax

Verifying Method Calls

import org.mockito.BDDMockito;

static <T> BDDMockito.BDDVerification<T> then(T mock)

Verifies that a method on a mock object was called with specific arguments.

Parameters:

• mock: The mock object whose method call is being verified.

Returns:

• A BDDVerification object that allows further verification.

Examples

Basic Usage

Use then to verify that a method on a mock object was called with specific arguments.

import static org.mockito.BDDMockito.*;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class BasicThenTest {
    @Test
    void testThen() {
        UserService mockUserService = mock(UserService.class);

        // Call the method
        mockUserService.getUserDetails("user123");

        // Verify the method call
        then(mockUserService).should().getUserDetails("user123");
    }
}

class UserService {
    public String getUserDetails(String userId) {
        return "Real user details for " + userId;
    }
}

Using then with Argument Matchers

Use then with argument matchers to verify that a method on a mock object was called with specific arguments.

import static org.mockito.BDDMockito.*;
import static org.mockito.ArgumentMatchers.*;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ThenWithArgumentMatchersTest {
    @Test
    void testThenWithArgumentMatchers() {
        UserService mockUserService = mock(UserService.class);

        // Call the method
        mockUserService.getUserDetails("user123");

        // Verify the method call with argument matchers
        then(mockUserService).should().getUserDetails(anyString());
    }
}

class UserService {
    public String getUserDetails(String userId) {
        return "Real user details for " + userId;
    }
}

Using then with Verification Modes

Use then with verification modes to verify that a method on a mock object was called a specific number of times.

import static org.mockito.BDDMockito.*;
import static org.mockito.Mockito.times;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ThenWithVerificationModesTest {
    @Test
    void testThenWithVerificationModes() {
        UserService mockUserService = mock(UserService.class);

        // Call the method multiple times
        mockUserService.getUserDetails("user123");
        mockUserService.getUserDetails("user123");

        // Verify the method call with a verification mode
        then(mockUserService).should(times(2)).getUserDetails("user123");
    }
}

class UserService {
    public String getUserDetails(String userId) {
        return "Real user details for " + userId;
    }
}

Real-World Use Case

Simplifying Tests for Services with Verification

In a real-world scenario, you might need to test services with methods that require verification of method calls. Using then can simplify these tests by allowing you to verify the method calls in a readable and intuitive way.

import static org.mockito.BDDMockito.*;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

interface EmailService {
    void sendEmail(String recipient, String subject, String body);
}

class UserService {
    private final EmailService emailService;

    public UserService(EmailService emailService) {
        this.emailService = emailService;
    }

    public void notifyUser(String userId, String message) {
        emailService.sendEmail(userId, "Notification", message);
    }
}

public class UserServiceTest {
    @Test
    void testNotifyUser() {
        EmailService mockEmailService = mock(EmailService.class);
        UserService userService = new UserService(mockEmailService);

        // Call the method
        userService.notifyUser("user123", "Your account has been updated.");

        // Verify the interaction
        then(mockEmailService).should().sendEmail("user123", "Notification", "Your account has been updated.");
    }
}

In this example, the UserServiceTest class uses Mockito’s BDDMockito.then method to verify that the sendEmail method was called with specific arguments. This simplifies the test by allowing you to specify the verification in a readable and intuitive way.

Conclusion

The BDDMockito.then method in Mockito is used for verifying that methods on mock objects were called with specific arguments in a BDD style. By using then, you can make your tests more readable and align them with the BDD approach, focusing on the behavior of the application rather than the implementation details. This helps ensure that your tests are clear, comprehensive, and easy to understand.