Add buffer attribute to DontReadFromInput

[joguSD]

Python 3 added a buffer attribute to sys.stdin. Simply accessing this attribute doesn't imply the program has read from stdin, as such this attribute should behave similarly to the stubbed input presently. This PR will add this property and return self such that attempting to read the buffer will raise exceptions the same as had you read from stdin.

[coveralls]

Coverage decreased (-0.008%) to 93.027% when pulling a152ea2 on joguSD:bugfix-stdin-stub-buffer into 3345ac9 on pytest-dev:master.

[RonnyPfannschmidt]

Well done

[nicoddemus]

That should have gone to features I think...

[The-Compiler]

I wondered about that as well - but to be fair, pytest patching sys.stdin with something which is different from what python does can count as a bug.

[nicoddemus]

Fair enough. 😁

[joguSD]

Thanks for the quick response! I'm not too familiar with Pytest's release cadence, is there an ETA on when this patch version will go out?

[nicoddemus]

We have a few regressions to fix but they shouldn't take long, so I would say sometime next week we could have a 3.0.2 release.

[joguSD]

Perfect, thanks again!