;
  document.firstElementChild.firstChild.setAttribute("foo", "bar");

  testing.eventually(() => {
    testing.expectEqual(1, nb);
    testing.expectEqual('attributes', mrs[0].type);
    testing.expectEqual(document.firstElementChild, mrs[0].target);
    testing.expectEqual('bar', mrs[0].target.getAttribute('foo'));
    testing.expectEqual('foo', mrs[0].attributeName);
    testing.expectEqual(null, mrs[0].oldValue);
  });

  var nb2 = 0;
  var mrs2;
  var node1 = $('#p1').firstChild;
  new MutationObserver