Mockito thenCallRealMethod Method

The thenCallRealMethod method in the Mockito framework is used to instruct a mock object to call the real implementation of a method when that method is invoked. This is particularly useful when you want to partially mock an object, allowing some methods to be mocked while others use their actual implementation.

Table of Contents

1. Introduction
2. thenCallRealMethod Method Syntax
3. Examples
   • Basic Usage
   • Using thenCallRealMethod with Partial Mocks
4. Real-World Use Case
5. Conclusion

Introduction

Mockito is a popular library in Java for creating and managing mock objects. The thenCallRealMethod method, which belongs to the OngoingStubbing interface, allows you to call the real implementation of a method on a mock object. This is useful when you want to mock certain behaviors while still using the actual implementation of some methods.

thenCallRealMethod Method Syntax

Setting the Real Implementation to be Called

import org.mockito.stubbing.OngoingStubbing;

OngoingStubbing<T> thenCallRealMethod()

Sets the real implementation to be called when the method is invoked on a mock object.

Returns:

• An OngoingStubbing object that allows further configuration of the stubbed method.

Examples

Basic Usage

Set the real implementation to be called for a stubbed method.

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

public class BasicThenCallRealMethodTest {
    @Test
    void testThenCallRealMethod() {
        UserService mockUserService = mock(UserService.class);

        // Set the real implementation to be called
        when(mockUserService.getUserDetails(anyString())).thenCallRealMethod();

        // Call the method
        String details = mockUserService.getUserDetails("123");
        assertEquals("Real user details for 123", details);
    }
}

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

Using thenCallRealMethod with Partial Mocks

Partially mock an object, allowing some methods to use their real implementation.

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

public class PartialMockTest {
    @Test
    void testPartialMock() {
        UserService mockUserService = mock(UserService.class);

        // Mock one method and set another to call the real implementation
        when(mockUserService.getUserDetails(anyString())).thenReturn("Mock user details");
        when(mockUserService.updateUser(anyString(), anyString())).thenCallRealMethod();

        // Call the methods
        String details = mockUserService.getUserDetails("123");
        String updateResponse = mockUserService.updateUser("123", "New Details");

        // Verify the results
        assertEquals("Mock user details", details);
        assertEquals("Updated user 123 with details New Details", updateResponse);
    }
}

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

    public String updateUser(String userId, String newDetails) {
        return "Updated user " + userId + " with details " + newDetails;
    }
}

Real-World Use Case

Using thenCallRealMethod in Service Mocks

In a real-world scenario, you might want to mock certain behaviors of a service while allowing other methods to use their actual implementation. This can be useful when you want to control specific behaviors without fully mocking the entire service.

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

interface PaymentService {
    String processPayment(String orderId, double amount);
    String getPaymentStatus(String orderId);
}

class PaymentServiceImpl implements PaymentService {
    public String processPayment(String orderId, double amount) {
        // Real implementation
        return "Payment processed for order " + orderId;
    }

    public String getPaymentStatus(String orderId) {
        // Real implementation
        return "Payment status for order " + orderId;
    }
}

public class PaymentServiceTest {
    @Test
    void testProcessPayment() {
        PaymentService mockPaymentService = mock(PaymentService.class);

        // Mock the processPayment method and use the real implementation for getPaymentStatus
        when(mockPaymentService.processPayment(anyString(), anyDouble())).thenReturn("Mock payment processed");
        when(mockPaymentService.getPaymentStatus(anyString())).thenCallRealMethod();

        // Call the methods
        String processResponse = mockPaymentService.processPayment("123", 100);
        String statusResponse = mockPaymentService.getPaymentStatus("123");

        // Verify the results
        assertEquals("Mock payment processed", processResponse);
        assertEquals("Payment status for order 123", statusResponse);
    }
}

In this example, the PaymentServiceTest class uses Mockito’s thenCallRealMethod to partially mock the PaymentService. The processPayment method is mocked to return a custom response, while the getPaymentStatus method uses the real implementation.

Conclusion

The thenCallRealMethod method in Mockito is used for setting up partial mocks. By using thenCallRealMethod, you can instruct a mock object to call the real implementation of a method, allowing for flexible and realistic testing scenarios. This helps ensure that your tests are accurate and comprehensive, allowing you to validate both real and mocked behavior.