Correct way to unit test a Mapper transformation method

Question

I have a Mapper class with one method which transforms one type of User to another type of User:

/**
 * Transform new {@link User} to legacy {@link com.xxx.xxx.bo.bean.User}.
 * @param user User to transform.
 * @return Transformed user.
 * @throws MappingException If an error occurred when transforming.
 */
public com.xxx.xxx.bo.bean.User transform(User user)
        throws MappingException {

    try {

        com.xxx.xxx.bo.bean.User legacyUser =
                new com.xxx.xxx.bo.bean.User();
        legacyUser.setIdUser(user.getIdUser());
        legacyUser.setIdUserType(user.getIdUserType());
        legacyUser.setName(user.getName());
        legacyUser.setSurname(user.getSurname());
        legacyUser.setEmail(user.getEmail());
        legacyUser.setUserAccount(user.getUserAccount());
        legacyUser.setPassword(user.getPassword());
        legacyUser.setUserType(user.getUserType());
        legacyUser.setIsOnlyAgent(user.isIsOnlyAgent());
        legacyUser.setAgentId(user.getAgentId());
        legacyUser.setIdVaAgent(user.getIdVaAgent());
        legacyUser.setDesktopUrl(user.getDesktopUrl());

        return legacyUser;

    } catch (Exception e){
        throw new MappingException("Error when mapping User to legacy User: "
                + e.getMessage());
    }
}

I have written a test to ensure that the mapping is made successfully:

@Test
public void GivenUser_WhenTransformToLegacyUser_LegacyUserIsReturned()
        throws Exception {

    final UUID userId = UUID.randomUUID();
    final UUID userTypeId = UUID.randomUUID();
    final String name = "name";
    final String surname = "surname";
    final String email = "email";
    final String userAccount = "user_account";
    final String password = "password";
    final String userType = "user_type";
    final boolean isOnlyAgent = getRandomBoolean();
    final UUID agentId = UUID.randomUUID();
    final UUID vaAgentId = UUID.randomUUID();
    final String desktopUrl = "desktop_url";

    final User user = mock(User.class);
    when(user.getIdUser()).thenReturn(userId);
    when(user.getIdUserType()).thenReturn(userTypeId);
    when(user.getName()).thenReturn(name);
    when(user.getSurname()).thenReturn(surname);
    when(user.getEmail()).thenReturn(email);
    when(user.getUserAccount()).thenReturn(userAccount);
    when(user.getPassword()).thenReturn(password);
    when(user.getUserType()).thenReturn(userType);
    when(user.isIsOnlyAgent()).thenReturn(isOnlyAgent);
    when(user.getAgentId()).thenReturn(agentId);
    when(user.getIdVaAgent()).thenReturn(vaAgentId);
    when(user.getDesktopUrl()).thenReturn(desktopUrl);

    com.xxx.xxx.bo.bean.User legacyUser =
            mMapper.transform(user);

    assertEquals(legacyUser.getIdUser(), userId);
    assertEquals(legacyUser.getIdUserType(), userTypeId);
    assertEquals(legacyUser.getName(), name);
    assertEquals(legacyUser.getSurname(), surname);
    assertEquals(legacyUser.getEmail(), email);
    assertEquals(legacyUser.getUserAccount(), userAccount);
    assertEquals(legacyUser.getPassword(), password);
    assertEquals(legacyUser.getUserType(), userType);
    assertEquals(legacyUser.isIsOnlyAgent(), isOnlyAgent);
    assertEquals(legacyUser.getAgentId(), agentId);
    assertEquals(legacyUser.getIdVaAgent(), vaAgentId);
    assertEquals(legacyUser.getDesktopUrl(), desktopUrl);
}

The problem is that this method is too verbose, my questions are:

Is this the proper way to unit test a transformation method in a Mapper class? Is there any other more elegant way to achive this?
I have a coleague who says that as this two models are POJOs and only contains sets() and gets(), it has no sense to verify each individual member, instead she would only test if the final transformed User is not null.

Thanks.

If you User classes are POJOs, why mock them at all? Also this: `throw new MappingException("Error when mapping User to legacy User: " + e.getMessage());` makes me cry - if the message of the exception is not self explanatory you won't even know what happened... — assylias, Jan 16 '18 at 11:32
You should pass real User parameter to transform method not mock object. You shouldn't mock any object for transform method. Mock operation is used for external services, database access vs. — ramazankul, Jan 16 '18 at 11:37
codereview.stackexchange.com may be more appropriate for questions about improving working code. But please read their help pages before asking there, to ensure your question matches their rules. — AdrianHHH, Jan 16 '18 at 12:01

score 6 · Answer 1 · answered Jan 16 '18 at 11:32

1) If you would try to unit test each single dto mapper in your app, that would be an overkill. In my experience only the most crucial DTO mappers are unit tested this way (and User usually is one of the key ones).

2) I wouldn't use mocks for the Input user. The general rule is, if you do not need to mock an object in a unit test, simply don't. That is a POJO, has no external dependencies and complex logic. Try to incorporate the builder pattern for creating dtos in your unit tests.

Correct way to unit test a Mapper transformation method

1 Answers1