How do I get my ActivityUnitTestCases to sync with the MessageQueue thread and call my Handler?

Question

I'm writing unit tests for a ListActivity in Android that uses a handler to update a ListAdapter. While my activity works in the Android emulator, running the same code in a unit test doesn't update my adapter: calls to sendEmptyMessage do not call handleMessage in my activity's Handler.

How do I get my ActivityUnitTestCase to sync with the MessageQueue thread and call my Handler?

The code for the Activity is somewhat like this:

public class SampleActivity extends ListActivity implements SampleListener {
    List samples = new ArrayList();

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.sample_list);
        listView.setEmptyView(findViewById(R.id.empty));
    }

    private final Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // unit test never reaches here
            sharesAdapter = new SampleAdapter(SampleActivity.this, samples);
            setListAdapter(sharesAdapter);
        }
    };

    public void handleSampleUpdate(SampleEvent event) {
        samples.add(event.getSample());
        handler.sendEmptyMessage(0);
    }
}

The code for my unit test is somewhat like this:

public class SampleActivityTest extends ActivityUnitTestCase<SampleActivity> {

    public SampleActivityTest() {
        super(SampleActivity.class);
    }

    @MediumTest
    public void test() throws Exception {
        final SampleActivity activity = startActivity(new Intent(Intent.ACTION_MAIN), null, null);
        final ListView listView = (ListView) activity.findViewById(android.R.id.list);
        activity.handleSampleUpdate(new SampleEvent(this));
        // unit test assert fails on this line:
        assertTrue(listView.getCount() == 1);
    }

}