cument.getElementById('para').innerHTML);
  testing.expectEqual('<span id="para-empty-child"></span>', $('#para-empty').innerHTML.trim());

  let h = $('#para-empty');
  const prev = h.innerHTML;
  h.innerHTML = '<p id="hello">hello world</p>';
  testing.expectEqual('<p id="hello">hello world</p>', h.innerHTML);
  testing.expectEqual('P', h.firstChild.nodeName);
  testing.expectEqual('hello', h.firstChild.id);
  testing.expectEqual('hello world', h.firstChild.textContent);

  h.innerHTML = prev;
  testing.e