Add capfdbinary fixture

[asottile]

capfdbinary works like capfd but produces bytes for readouterr().

See #2923

[asottile]

CC @nicoddemus

I approached this only from the capfd front, it's slightly more involved to implement this for capsys (because python2 capture io is not predictably typed) -- I think this is fine, capfd is more useful in this case anyway.

Feedback appreciated, I threw this together quickly and might've missed some documentation / naming / etc.

[nicoddemus]

Thanks a lot @asottile, that was quick! 👍

it's slightly more involved to implement this for capsys (because python2 capture io is not predictably typed)

This is fine, but it is easy to implement capsys-like for Python 3? IMHO it is fine to add Python 3-only functionality if reasonably easy (doesn't depend on new syntax for example). Not sure how others feel about this, but it is time to start considering Python 3 only features when it is not feasible to support them in Python 2.

[nicoddemus]

Awesome work!

I left some small comments, but overall this is top-notch.

[nicoddemus]

I would prefer to use "fixtures" instead of "function argument".

[asottile]

👍 , while writing this I myself wrote "fixtures" but then matched it with the paragraph above -- I'll update both of them

[nicoddemus]

Please add here, before the next paragraph:

.. versionadded:: 3.3

[asottile]

Yeah capsysbinary is pretty easy to implement in python 3 due to the work I did in #2266 (CaptureIO maintains .buffer), it's only difficult because in python2 CaptureIO is TextIO (backed by io.StringIO) which doesn't actually expose a binary storage.

[nicoddemus]

Yeah capsysbinary is pretty easy to implement in python 3

I'm OK with making capsysbinary available only in Python 3. We should make it explicit in the docs and using the fixture in Python 2 should raise an error.

But let's see what others think about this first.

[coveralls]

Coverage decreased (-0.003%) to 92.694% when pulling 123e4f6 on asottile:capfdbinary into 685387a on pytest-dev:features.

[coveralls]

Coverage decreased (-0.002%) to 92.695% when pulling 8f90812 on asottile:capfdbinary into 685387a on pytest-dev:features.

[RonnyPfannschmidt]

we can start with python3 only, but we should take a look at exposing a encoded bytesio kinda thing in future

[nicoddemus]

@asottile so I guess we can go ahead with capsysbinary for py3 only then. 👍

[asottile]

@nicoddemus cool, ok for me to do that in a followup?

[RonnyPfannschmidt]

@asottile yup

[nicoddemus]

@RonnyPfannschmidt want some more time to take look at this?

Otherwise I will merge this tomorrow. 👍

[nicoddemus]

Thanks again @asottile!