((mu) => {
      mrs2 = mu;
      nb2++;
  }).observe(node1, { characterData: true, characterDataOldValue: true });
  node1.data = "foo";

  testing.eventually(() => {
    testing.expectEqual(1, nb2);
    testing.expectEqual('characterData', mrs2[0].type);
    testing.expectEqual(node1, mrs2[0].target);
    testing.expectEqual('foo', mrs2[0].target.data);
    testing.expectEqual(' And', mrs2[0].oldValue);
  });
</script>

<script id=callback>
  // tests that mutation observers that have a callback which tri