testGetRequiredElementByClassDomHelper() {
    const domHelper = new DomHelper();
    assertNotNull(domHelper.getRequiredElementByClass('test1'));
    assertNotNull(domHelper.getRequiredElementByClass('test2'));

    const container = domHelper.getElement('span-container');
    assertNotNull(domHelper.getElementByClass('test1', container));
    assertThrows(/**
                    @suppress {checkTypes} suppression added to enable type
                    checking
                  */
                 () => {
                   domHelper.getRequiredElementByClass(
                       'does_not_exist', container);
                 });
  }
@suppress {undefinedVars} suppression added to enable type
                    checking