 = srcdocThatPostsParentOpener("srcdoc2");

  // Test that it's a push back to about:srcdoc.
  await waitForMessage(iframe.contentWindow);
  assert_equals(
    w.history.length,
    4,
    "history.length must increase since it was a push"
  );
  assert_equals(iframe.contentWindow.location.href, "about:srcdoc");
  assert_equals(
    iframe.contentDocument.querySelector("p").textContent,
    "srcdoc2",
    "Sanity check: the srcdoc document did indeed update"
  );

  // Test that we can go back to about:srcd