Testing a method which uses another method from the same class

Question

Recently I have gotten into unit testing my applications and have found myself at a bit of a difficult spot design wise in one of my classes.

I have a repository class which connects to the database, which looks a bit like this.

public interface Repository {
  ...
  void register(Account account)
  Account find(String email)
  ...
}

which, in implementation does this:

public class RepositoryImpl implements Repository {
  ...
  public void register(Account account) {
    if (find(account.getEmail() != null) return;
    // Account with same email already exists.
    ...
  }
}

This works fine in a live setting, but when unit testing it's a different story.

I use Mockito for mocking my dependencies, but I cant seem to mock the find method in the implementation class.

So my first thought was to inject a Repository in the register method which I than can fake, but that seems a bit weird since I provide a method with a class which it is a member of itself.

After that I thought to just copy the find logic to the register method, but that violates the DRY principle.

So.. any ideas on solving this design problem? I guess it's a common problem since it's quite standard to have unique emails in a system.

Thanks!

Answer 1

If you want to mock a method of the class under test you would need to spy it instead of using a concrete implementation:

// arrange
Account acc = new Account();
RepositoryImpl repoSpy = Mockito.spy(new RepositoryImpl());

doReturn(acc).when(repoSpy).find(Mockito.any(String.class));

//act
repoSpy.register(acc);

// assert ..

Thanks to that the register implementation will be used and the find method will be mocked to you liking.