ViewInteraction.java

public ViewInteraction check(ViewAssertion viewAssertion) {
    // (...)
    runSynchronouslyOnUiThread(new Callable<Void>() {
        @Override
        public Void call() {
            uiController.loopMainThreadUntilIdle();
            // (...)
            viewAssertion.check(...)
        }
    });
}