Capturing a Runnable with JMockit and Executing It

At work, we use JMockit. I’m far more comfortable with Mockito, which made it very easy for me to understand how to capture a Runnable passed in, execute it, and then check that certain calls were made. I have always struggled with doing that with JMockit, but I think I finally figured it out:

public class DemoWithRunnable { public interface Dependency { int someMethod(); void otherMethod(int i); }


    private final Dependency dependency;

    private final ExecutorService executor;
    public DemoWithRunnable(Dependency d, ExecutorService e) {

        this.dependency = d;

        this.executor = e;

    }

public void doSomething() { executor.submit(new Runnable() { public void run() { int i = dependency.someMethod(); dependency.otherMethod(i); } }); } }

What I want to do here in a test, of course, is:

Check that we call ExecutorService.submit
Run the Runnable that was passed to submit
Mock someMethod and return some value, and
Check that otherMethod was called with the returned value.

And I think this is how you do it in JMockit:

public class DemoWithRunnableTest { @Mocked DemoWithRunnable.Dependency d;


    @Mocked ExecutorService e;
    @Test

    public void testDoSomething() {

        DemoWithRunnable impl = new DemoWithRunnable(d, e);
        impl.doSomething();
        List r = new ArrayList<>();
        // capture the Runnable

        new Verifications() {{

            e.submit(withCapture(r));

        }};
        // add new expectations for code in the Runnable, with return values

        new Expectations() {{

            d.someMethod(); result = 42;

        }};
        // run the Runnable

        r.get(0).run();