alled");
  i.contentWindow.navigation.onnavigateerror = t.unreached_func("onnavigateerror should not be called");

  let assertionPromise;
  // The iframe does not have sticky activation, so per
  // https://html.spec.whatwg.org/#prompt-to-unload-a-document, no prompt is
  // shown and the navigation will proceed.
  i.contentWindow.onbeforeunload = t.step_func(() => {
    assertionPromise = assertBothRejectDOM(t, i.contentWindow.navigation.navigate("#"), "InvalidStateError", i.contentWindow);
  });
  i.cont