How to check if refresh token is expired with the SDK for iOS - Amazon Cognito?

Refresh token expiration day was set on Amazon Cognito.

I tried them after Refresh token expiration date.

user!.isSignedIn
user!.getSession().result

However it seems they don't work for checking refresh token is expired or not.

If you can give me any advice or tips, please tell me. I would really appreciate it. Thank you in advance.