@Test
public void testTransformUserCollection() {

    User mockUserOne = mock(User.class);
    User mockUserTwo = mock(User.class);

    List<User> userList = new ArrayList<>(5);
    userList.add(mockUserOne);
    userList.add(mockUserTwo);

    Collection<UserModel> userModelList = userModelDataMapper.transform(userList);

    assertThat(userModelList.toArray()[0], is(instanceOf(UserModel.class)));
    assertThat(userModelList.toArray()[1], is(instanceOf(UserModel.class)));
    assertThat(userModelList.size(), is(2));
}