function assertAdminEmail(adminEmail) {
  const element = goog.dom.getElementByClass(
      'firebaseui-id-unauthorized-user-admin-email', container);
  assertNotNull(element);
  if (adminEmail) {
    assertContains(adminEmail, goog.dom.getTextContent(element));
  }
}
Asserts that there is an admin email currently displayed.
@param {string=} adminEmail admin email to check.