How to write unit tests for classes with CheckedProviders in their constructors

Question

I have a class under test whose constructer looks like this :

public class ClassUnderTest {

ClientOne clientOne;
ClientTwo clientTwo;
OtherDependency otherDependency; 

@Inject
public ClassUnderTest(MyCheckedProvider<ClientOne> myCheckedProviderOne,
                   MyCheckedProvider<ClientTwo> myCheckedProviderTwo,
                   OtherDependency otherDependency) throws Exception {
       this.clientOne = myCheckedProviderOne.get();
       this.clientTwo = myCheckedProviderTwo.get();
       this.otherDependency = otherDependency; 
   }
    .
    .
    .
}

And the CheckedProvider looks thus :

public interface MyCheckedProvider<T> extends CheckedProvider<T> {

  @Override
  T get() throws Exception;

}

I could mock the clients, but how do I initialise the providers with my mocked clients.I use a combination of junit and mockito for writing tests.Any inputs would be appreciated.

Answer 1

What you could do is to mock providers rather than clients. ClientOne and ClientTwo are the types you are passing into your generic class, they are not variables and hence not something you want to mock. In contrast, the providers you are passing to the constructor are really variables, and what you need to control (simulate) are the behaviors of these variables.

public class ClassTest {

    private static final CientOne CLIENT_ONE = new ClientOne();
    private static final ClientTwo CLIENT_TWO = new ClientTwo();

    @Mock
    private MyCheckedProvider<ClientOne> providerOne;

    @Mock
    private MycheckedProvider<ClientTwo> providerTwo;

    private ClassUnderTest classUnderTest;

    @Before
    public void setUp() {
        when(providerOne.get()).thenReturn(CLIENT_ONE);
        when(providerTwo.get()).thenReturn(CLIENT_TWO);
        classUnderTest = new ClassUnderTest(providerOne, providerTwo, otherDependency);
    }
}

Answer 2

As the other answer suggests, you could easily mock the providers, too.

But youMyCheckedProvider don't have to.

You already have an interface sitting there, so what would prevent you from creating something like

class MyCheckedProviderImpl<T> implements MyCheckedProvider<T> {

and that think takes a T object in its constructor and returns exactly that?

That is more or less the same what the mocking framework would be doing.