Q:

Testing Using NUnit and Moq: use case

I have a business class that manage a USER entity.
In this class I have a method to return a single user by id:
public Utente GetUser(int id)
{
    var utente = _userDataManager.GetUserById(id);

    return _mapper.Map<Utente>(utente);
}

_userDataManager is an interface, IUSERDATAMANAGER, and it has implemented with a DAL class; GetUserById return a user or null (search made with EF6).
_mapper is a IMAPPER interface (automapper).
The method return is the mapped object.
I have two question:

Does it make sense to test this method?
Should I mock both the object?

A black-boxed example will be appreciated.

A:

Does it make sense to test this method?

If it is worth writing the code it is worth testing the code.

Should I mock both the object?

When testing a subject under test, you mock the dependencies that would allow the test to be exercised to completion.
For example
public void GetUser_Should_Return_Utente() {
    //Arrange
    var userId = 2;
    var user = new User {
        UserId = userId,
        //... other properties
    };
    var userDataManagerMock = new Mock<IUserDataManager>();
    userDataManagerMock.Setup(_ => _.GetUserById(userId)).Returns(user);

    var expected = new Utente {
        Id = user.Id,
        //...other properties
    }

    var mapperMock = new Mock<IMapper>();
    mapperMock.Setup(_ => _.Map<Utente>(It.IsAny<object>())).Returns(expected);

    var subject = new MyBusinessClass(userDataManagerMock.Object, mapperMock.Object);

    //Act
    var actual = subject.GetUser(userId);

    //Assert
    Assert.Equal(expected, actual);
}

In the above code the user data manager and the mapper a mocked and injected into the subject when testing the GetUser method. 
This is an isolated unit test of the above method and shows the the current implementation of that method will flow to completion provided the dependencies perform as expected during invocation.

