ProgressBars and Espresso

If the ProgressBar is invisible when the test starts, the Drawable can be replaced with by a custom ViewAction:

// Replace the drawable with a static color
onView(isAssignableFrom(ProgressBar.class)).perform(replaceProgressBarDrawable());

// Click a button (that will make the ProgressBar visible)
onView(withText("Show ProgressBar").perform(click());

The custom ViewAction:

public static ViewAction replaceProgressBarDrawable() {
    return actionWithAssertions(new ViewAction() {
        @Override
        public Matcher<View> getConstraints() {
            return isAssignableFrom(ProgressBar.class);
        }

        @Override
        public String getDescription() {
            return "replace the ProgressBar drawable";
        }

        @Override
        public void perform(final UiController uiController, final View view) {
            // Replace the indeterminate drawable with a static red ColorDrawable
            ProgressBar progressBar = (ProgressBar) view;
            progressBar.setIndeterminateDrawable(new ColorDrawable(0xffff0000));
            uiController.loopMainThreadUntilIdle();
        }
    });
}