Using Mockito to test abstract classes

Question

I'd like to test an abstract class. Sure, I can manually write a mock that inherits from the class.

Can I do this using a mocking framework (I'm using Mockito) instead of hand-crafting my mock? How?

Answer 1

The following suggestion let's you test abstract classes without creating a "real" subclass - the Mock is the subclass.

use Mockito.mock(My.class, Mockito.CALLS_REAL_METHODS), then mock any abstract methods that are invoked.

Example:

public abstract class My {
  public Result methodUnderTest() { ... }
  protected abstract void methodIDontCareAbout();
}

public class MyTest {
    @Test
    public void shouldFailOnNullIdentifiers() {
        My my = Mockito.mock(My.class, Mockito.CALLS_REAL_METHODS);
        Assert.assertSomething(my.methodUnderTest());
    }
}

Note: The beauty of this solution is that you do not have to implement the abstract methods, as long as they are never invoked.

In my honest opinion, this is neater than using a spy, since a spy requires an instance, which means you have to create an instantiatable subclass of your abstract class.