mockito Getting started with mockito Verifying arguments with ArgumentCaptor

Example

To validate arguments to methods called on a mock, use the ArgumentCaptor class. This will allow you to extract the arguments into your test method and perform assertions on them.

This example tests a method which updates the name of a user with a given ID. The method loads the user, updates the name attribute with the given value and saves it afterwards. The test wants to verify that the argument passed to the save method is a User object with the correct ID and name.

// This is mocked in the test
interface UserDao {
    void save(User user);
}

@RunWith(MockitoJUnitRunner.class)
public class UserServiceTest {
    @Mock
    UserDao userDao;

    @Test
    public void testSetNameForUser() {
        UserService serviceUnderTest = new UserService(userDao);
        
        serviceUnderTest.setNameForUser(1L, "John");

        ArgumentCaptor<User> userArgumentCaptor = ArgumentCaptor.forClass(User.class);
        
        verify(userDao).save(userArgumentCaptor.capture());
        User savedUser = userArgumentCaptor.getValue();
        assertTrue(savedUser.getId() == 1);
        assertTrue(savedUser.getName().equals("John"));
    }
}