('div');
  document.body.appendChild(popover);

  assert_throws_dom('NotSupportedError', () => popover.togglePopover(),
    'togglePopover() should throw an exception when the element has no popover attribute.');
  assert_throws_dom('NotSupportedError', () => popover.togglePopover(true),
    'togglePopover(true) should throw an exception when the element has no popover attribute.');
  assert_throws_dom('NotSupportedError', () => popover.togglePopover(false),
    'togglePopover(false) should throw an excepti