I was able to run almost all samples using new accounts I created for this test. I used basic operations listed in the doc and that was pretty straightforward.

I had an issue, though, using my Google account when trying to get my gmail.

I clicked on Log In and entered my Google account in the separate screen that opened up
After pressing Accept on the screen below, I got a token - good.
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I used drive/v2/files in operation and it listed folder/file information - good.

Used gmail/v1/users/me/messages and it returned:
"code": 403,
"message": "Insufficient Permission"

Is that expected?