function assertDialog(message) {
  assertEquals(1, goog.dom.getElementsByTagName('dialog').length);
  var dialogElement = goog.dom.getElementsByTagName('dialog')[0];
  assertTrue(
      goog.dom.classlist.contains(dialogElement, 'firebaseui-id-dialog'));
  assertContains(message, goog.dom.getTextContent(dialogElement));
}
Asserts that the dialog is rendered with the expected message.
@param {string} message The message shown.