Mockito anyList Method

The anyList method in the Mockito framework is part of the ArgumentMatchers class. It is used to match any non-null List as an argument in mocked methods. This is particularly useful when you do not care about the specific list being passed as an argument in a method call.

Table of Contents

1. Introduction
2. anyList Method Syntax
3. Examples
   • Basic Usage
   • Using anyList in Different Scenarios
4. Real-World Use Case
5. Conclusion

Introduction

Mockito is a popular library in Java for creating and managing mock objects. The anyList method, which belongs to the ArgumentMatchers class, allows you to specify that any non-null List should match an argument in a mocked method. This can be useful for simplifying tests where the specific content of the list is not important.

anyList Method Syntax

Matching Any Non-Null List

import org.mockito.ArgumentMatchers;

static <T> List<T> anyList()

Matches any non-null List.

Returns:

• A List of type T that matches any non-null list argument.

Examples

Basic Usage

Use anyList to match any non-null list argument in a mocked method call.

import static org.mockito.Mockito.*;
import org.mockito.ArgumentMatchers;
import org.junit.jupiter.api.Test;
import java.util.List;
import static org.junit.jupiter.api.Assertions.*;

public class BasicAnyListTest {
    @Test
    void testAnyList() {
        UserService mockUserService = mock(UserService.class);

        // Stub the method to return a specific value
        when(mockUserService.processUsernames(ArgumentMatchers.anyList())).thenReturn("Processed usernames");

        // Call the method with different list arguments
        String result1 = mockUserService.processUsernames(List.of("user1", "user2"));
        String result2 = mockUserService.processUsernames(List.of("user3", "user4"));

        // Verify the results
        assertEquals("Processed usernames", result1);
        assertEquals("Processed usernames", result2);
    }
}

class UserService {
    public String processUsernames(List<String> usernames) {
        return "Real processing of usernames: " + usernames.toString();
    }
}

Using anyList in Different Scenarios

Use anyList to match list arguments in methods with multiple parameters.

import static org.mockito.Mockito.*;
import org.mockito.ArgumentMatchers;
import org.junit.jupiter.api.Test;
import java.util.List;
import static org.junit.jupiter.api.Assertions.*;

public class AnyListWithMultipleParametersTest {
    @Test
    void testAnyListWithMultipleParameters() {
        NotificationService mockNotificationService = mock(NotificationService.class);

        // Stub the method to return specific values
        when(mockNotificationService.sendNotifications(ArgumentMatchers.anyString(), ArgumentMatchers.anyList())).thenReturn("Notifications sent");

        // Call the method with different arguments
        String result1 = mockNotificationService.sendNotifications("Info", List.of("email1", "email2"));
        String result2 = mockNotificationService.sendNotifications("Alert", List.of("email3", "email4"));

        // Verify the results
        assertEquals("Notifications sent", result1);
        assertEquals("Notifications sent", result2);
    }
}

interface NotificationService {
    String sendNotifications(String type, List<String> recipients);
}

Real-World Use Case

Simplifying Tests for Services with List Parameters

In a real-world scenario, you might need to test services with methods that take list parameters. Using anyList can simplify these tests by allowing you to focus on the behavior you are testing rather than the specific content of the lists.

import static org.mockito.Mockito.*;
import org.mockito.ArgumentMatchers;
import org.junit.jupiter.api.Test;
import java.util.List;
import static org.junit.jupiter.api.Assertions.*;

interface DataService {
    void saveData(String entity, List<String> data);
}

class DataProcessor {
    private final DataService dataService;

    public DataProcessor(DataService dataService) {
        this.dataService = dataService;
    }

    public void processAndSaveData(String entity, List<String> data) {
        // Process data logic
        dataService.saveData(entity, data);
    }
}

public class DataProcessorTest {
    @Test
    void testProcessAndSaveData() {
        DataService mockDataService = mock(DataService.class);
        DataProcessor dataProcessor = new DataProcessor(mockDataService);

        // Call the method
        dataProcessor.processAndSaveData("Entity1", List.of("data1", "data2"));
        dataProcessor.processAndSaveData("Entity2", List.of("data3", "data4"));

        // Verify the interaction
        verify(mockDataService, times(2)).saveData(anyString(), ArgumentMatchers.anyList());
    }
}

In this example, the DataProcessorTest class uses Mockito’s anyList method to match any non-null list argument for the saveData method. This simplifies the test by allowing you to verify the interaction without specifying the exact content of the lists.

Conclusion

The anyList method in Mockito is used for matching any non-null list as an argument in mocked method calls. By using anyList, you can simplify your tests and focus on the behavior you are testing, rather than the specific content of the lists. This helps ensure that your tests are flexible, comprehensive, and easy to maintain.