Argument matchers (any, eq) in JUnit - Test Execution Trace

Test Overview

This test verifies that a method is called with specific argument values using eq() and any argument using any() matchers in JUnit with Mockito. It checks that the service method behaves correctly when called with expected parameters.

Test Code - JUnit with Mockito

JUnit

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

import org.junit.jupiter.api.Test;
import org.mockito.Mockito;

interface UserRepository {
    String findRole(String userId, Boolean active);
}

class UserService {
    UserRepository repo;
    UserService(UserRepository repo) {
        this.repo = repo;
    }
    String getUserRole(String userId, boolean active) {
        return repo.findRole(userId, active);
    }
}

public class UserServiceTest {
    @Test
    void testGetUserRoleWithArgumentMatchers() {
        UserRepository mockRepo = Mockito.mock(UserRepository.class);
        when(mockRepo.findRole(eq("user123"), any(Boolean.class))).thenReturn("admin");

        UserService service = new UserService(mockRepo);
        String role = service.getUserRole("user123", true);

        assertEquals("admin", role);
        verify(mockRepo).findRole(eq("user123"), any(Boolean.class));
    }
}

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	Mockito mock UserRepository created	Mock object ready to intercept calls	-	PASS
3	Stub findRole method with eq("user123") and any(Boolean.class) to return "admin"	Mock configured to return 'admin' for matching arguments	-	PASS
4	UserService instance created with mock repository	Service ready to call mocked method	-	PASS
5	Call getUserRole("user123", true)	Method calls mockRepo.findRole("user123", true)	Check that findRole is called with eq("user123") and any(Boolean.class)	PASS
6	Assert returned role equals "admin"	Role variable holds method return value	assertEquals("admin", role)	PASS
7	Verify mockRepo.findRole called with eq("user123") and any(Boolean.class)	Mockito verifies method call arguments	verify(mockRepo).findRole(eq("user123"), any(Boolean.class))	PASS
8	Test ends successfully	All assertions passed	-	PASS

Failure Scenario

Failing Condition: The findRole method is called with arguments that do not match eq("user123") or any(Boolean.class), or the stub is not set correctly.

Execution Trace Quiz - 3 Questions

What does the matcher eq("user123") do in this test?

A Allows any string argument

B Checks that the argument is not null

C Checks that the argument exactly equals "user123"

D Matches any Boolean argument

Key Result

When using Mockito argument matchers like eq() and any(), always use matchers for all arguments in a method call to avoid errors and ensure precise verification.