function getTestIframeIo() {
  logconsole.addSeparator();
  logconsole.getFormatter().resetRelativeTimeStart();

  const io = new IframeIo();
  io.setErrorChecker(checkForError);

  events.listen(io, 'success', onSuccess);
  events.listen(io, 'error', onError);
  events.listen(io, 'ready', onReady);

  return io;
}
Creates an iframeIo instance and sets up the test environment.
@return {!IframeIo}