How do I test interactions with GTMOAuth2Authentication?

I'm making changes to an iOS app that uses Google Toolbox for Mac OAuth 2 to access Google Calendar.

After making my change I can see the "happy path" works fine, but how do I test conditions where my token has expired and is automatically renewed, vs token expired and stale (forcing a re-authentication) etc?

Does the OAuth 2 Playground help me at all? How?