Mocking dependency that has setListener(...)

My class under test has a few dependencies. All of these provide setListener() as a way to receiving notification from their non-blocking operations.

I implemented a blocking method that aggregates the results from all the non-blocking ops. Which mean I have to register the listeners using such setListener() methods, and wait for the callbacks.

How should I mock/fake these dependencies in my unit test? I could subclass them and implement setListener() and fire the callbacks as necessary. But let's say some of these deps are final class. Also, I think there might be something I could use from Mockito?

Conceptual code (untested):

public void blockingMethod() {
  CountDownLatch signal = new CountDownLatch(2);

  dep1.setListener(new Dep1Listener() {
    @Override public onResult(int result) {
      signal.countDown();
    }
  });
  dep1.calculateValue1();

  dep2.setListener(new Dep2Listener() {
    @Override public onResult(int result) {
      signal.countDown();
    }
  });
  dep2.calculateValue2();

  signal.await();
  return combinedResult;
}