code: public static int addDisplay(String qualifiersStr) {
      int id = getShadowDisplayManagerGlobal().addDisplay(createDisplayInfo(qualifiersStr, null));
      shadowMainLooper().idle();
      return id;
    }
docs: Adds a simulated display and drain the main looper queue to ensure all the callbacks are
  processed.
  
  @param qualifiersStr the {@link Qualifiers} string representing characteristics of the new
  display.
  @return the new display's ID