Mockito BDDMockito given Method

The given method in the BDDMockito class is part of the Behavior-Driven Development (BDD) style of writing tests using Mockito. It is used to set up expectations on mock objects. 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. given Method Syntax
3. Examples
   • Basic Usage
   • Using given with Different Return Values
   • Using given with Exceptions
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 given method is used to set up expectations on mock objects in a more readable way.

given Method Syntax

Setting Up Expectations

import org.mockito.BDDMockito;

static <T> BDDMockito.BDDMyOngoingStubbing<T> given(T methodCall)

Sets up an expectation on a mock object.

Parameters:

• methodCall: The method call on the mock object for which the expectation is being set.

Returns:

• A BDDMyOngoingStubbing object that allows further stubbing.

Examples

Basic Usage

Use given to set up a basic expectation on a mock object.

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

public class BasicGivenTest {
    @Test
    void testGiven() {
        UserService mockUserService = mock(UserService.class);

        // Set up the expectation
        given(mockUserService.getUserDetails("user123")).willReturn("Mock user details");

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

        // Verify the result
        assertEquals("Mock user details", result);
    }
}

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

Using given with Different Return Values

Use given to set up expectations with different return values.

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

public class GivenDifferentReturnValuesTest {
    @Test
    void testGivenDifferentReturnValues() {
        UserService mockUserService = mock(UserService.class);

        // Set up the expectations
        given(mockUserService.getUserDetails("user123")).willReturn("Mock user details for user123");
        given(mockUserService.getUserDetails("user456")).willReturn("Mock user details for user456");

        // Call the methods
        String result1 = mockUserService.getUserDetails("user123");
        String result2 = mockUserService.getUserDetails("user456");

        // Verify the results
        assertEquals("Mock user details for user123", result1);
        assertEquals("Mock user details for user456", result2);
    }
}

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

Using given with Exceptions

Use given to set up expectations that throw exceptions.

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

public class GivenWithExceptionTest {
    @Test
    void testGivenWithException() {
        UserService mockUserService = mock(UserService.class);

        // Set up the expectation to throw an exception
        given(mockUserService.getUserDetails("user123")).willThrow(new RuntimeException("User not found"));

        // Call the method and verify the exception
        Exception exception = assertThrows(RuntimeException.class, () -> {
            mockUserService.getUserDetails("user123");
        });
        assertEquals("User not found", exception.getMessage());
    }
}

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

Real-World Use Case

Simplifying Tests for Services with Complex Behaviors

In a real-world scenario, you might need to test services with methods that have complex behaviors. Using given can simplify these tests by allowing you to set up expectations 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) {
        if (userId == null) {
            throw new IllegalArgumentException("User ID cannot be null");
        }
        emailService.sendEmail(userId, "Notification", message);
    }
}

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

        // Set up the expectation
        willDoNothing().given(mockEmailService).sendEmail("user123", "Notification", "Your account has been updated.");

        // 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.given method to set up an expectation on the sendEmail method. This simplifies the test by allowing you to set up and verify interactions in a readable and intuitive way.

Conclusion

The BDDMockito.given method in Mockito is used for setting up expectations on mock objects in a BDD style. By using given, 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.