未调用Android InstrumentationTestCase runTestOnUiThread

Question

我正在尝试在InstrumentationTestCase中的UI线程上运行非常简单的代码，但它从未调用过。例如，此测试通过。我怎样才能正确运行？

public class Test1 extends InstrumentationTestCase {

    @Test
    public void testUI() throws Throwable {
        final CountDownLatch signal = new CountDownLatch(1);

        runTestOnUiThread(new Runnable() {
            @Override
            public void run() {
               fail();
            }

        });

        try {
            signal.await(30, TimeUnit.SECONDS); // wait for callback
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}