@Test
public void startOnce() {

    List<Throwable> error = TestHelper.trackPluginErrors();
    try {
        TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
        final SerializedSubscriber<Integer> so = new SerializedSubscriber<Integer>(ts);
        so.onSubscribe(new BooleanSubscription());
        BooleanSubscription d = new BooleanSubscription();
        so.onSubscribe(d);
        assertTrue(d.isCancelled());
        TestHelper.assertError(error, 0, IllegalStateException.class, "Subscription already set!");
    } finally {
        RxJavaPlugins.reset();
    }
}