ho.appendChild(s1);
  flush();
  assert.equal(container.children.length, 2);
  assert.equal(echo.nextElementSibling, s2);
  echo.appendChild(s2);
  flush();
  assert.equal(container.children.length, 1);
  assert.equal(echo.nextElementSibling, null);
  container.appendChild(s1);
  flush();
  assert.equal(container.children.length, 2);
  assert.equal(echo.nextElementSibling, s1);
  container.appendChild(s2);
  flush();
  assert.equal(container.children.length, 3);
  assert.equal(echo.nextElementSibling, s1);
