Best approach for verifying a FutureCallback effect with Jmockit

What is the preferred mechanism for verifying the effects of a callback in Jmockit?

For example, assume I have this class.

class ResultGenerator {
    AsyncLauncher asyncLauncher = new AsyncLauncher();

    public void getResultAsync(final ResultSignal resultSignal) {
        asyncLauncher.getResult(new FutureCallback<Result>() {
                @Override
                public void onSuccess(@Nullable Result result) {
                    resultSignal.success(result);
                }

                @Override
                public void onFailure(Throwable t) {
                    resultSignal.failure();
                }
        });
    }
}

How do I verify bar.success(result) when writing a test for FooGenerator#getResultAsync?