testGetKeyHandler() {
    assertUndefined(
        'Key handler must be undefined before getKeyHandler() ' +
            'is called',
        control.keyHandler_);
    /** @suppress {visibility} suppression added to enable type checking */
    const keyHandler = control.getKeyHandler();
    assertNotNull('Key handler must not be null', keyHandler);
    assertEquals(
        'getKeyHandler() must return the same instance if called ' +
            'again',
        keyHandler, control.getKeyHandler());
  }
Tests {@link Control#getKeyHandler}.
@suppress {visibility} suppression
     added to enable type checking