How to obtain a reference to a Runnable instance passed to a Thread constructor using PowerMock(ito)?

There's a black box class which creates a Thread using its constructor accepting an instance of Runnable as the argument:

public class Service {

  public static Task implements Runnable {

    @Override
    public void run() {

      doSomeHeavyProcessing();
    }
  }

  public void doAsynchronously() {

    new Thread(new Task()).start();
  }
}

I want to intercept the constructor call and get a reference to the passing Task implementing Runnable. This is the code so far:

@RunWith(PowerMockRunner.class)
@PrepareForTest(Service.class)
public class ServiceTest {

  @Test
  public void testService() {

    ArgumentCaptor<Runnable> runnables = ArgumentCaptor.forClass(Runnable.class);
    Thread thread = Mockito.mock(Trhead.class);
    whenNew(Thread.class.getContructor(Runnable.class)).
      withArguments(runnables.capture)).thenReturn(thread);

    new Service().doAsynchronously();

    System.out.println("all runnables: " + runnables.getAllValues());

    for (Runnable r : runnables.getAllValues()) r.run();

    // perform some assertions after the code meant to be executed in a new
    // thread has开发者_开发百科 been executed in the current (main) thread
  }
}

Test execution will print out:

all runnables: []

Is there a way of grabbing a reference to all Runnable objects or Thread objects returned by the constructor? I want to execute the asynchronous code either in the current (main) thread or join created threads and perform assertions.

---

First your code had some typo errors, and once corrected it didn't work when tried in the IDE. The code throws a VerifyError about the Task initialization. Making Task public helped.

Once every was alright, your code worked as expected, meaning your runnables were captured.

Although I would go for this stubbing syntax instead :

whenNew(Thread.class).withParameterTypes(Runnable.class)
    .withArguments(runnables.capture()).thenReturn(mock);

You should investigate your real code to see if it got correctly stubbed.