[pytest-dev] What's the best way of writing tests for terminal width resize behaviour in an assertrepr plugin?

[Harry Percival]

Floris, that's exactly the answer I was most afraid of. oh no.

Zach, great minds!  any thoughts on what i've done so far in my plugin,
things i've missed, things i could add?
https://github.com/hjwp/pytest-icdiff

On Thu, 9 Apr 2020 at 04:48, Zach Kanzler <they4kman at gmail.com> wrote:

> I wrote an icdiff-based pretty diffs pytest plugin for internal use, and
> ran into the same issue. I ended up grabbing the terminal width at
> module-level, as well. I think I went spelunking in the GH issues and found
> a glimmer of possibility in the notion that get_terminal_width() returns
> incorrect information from within the assertrepr hook, because it's
> called when terminal capturing is enabled — perhaps even just a wrapped
> stream?
>
> Here's the note I left myself:
>
> # This is done during initialization, before any tests are run, instead of
> # within our assertrepr hook — because the assertrepr hook is called while
> # terminal capturing is enabled and all calls to get_terminal_width()
> return 80
> # ref:
> https://github.com/pytest-dev/pytest/issues/4030#issuecomment-425672782
> INITIAL_TERM_WIDTH, INITIAL_TERM_HEIGHT = util.get_terminal_size()
>
>
> (Where util.get_terminal_size() just comes from this gist
> <https://gist.github.com/jtriley/1108174>)
>
> I wonder if a tool like screen or tmux could supply real sizing info and
> resize events, while also appearing like an unwrapped stream — and perhaps
> its output could be saved & compared against.
>
> Cheers,
> Zach
>
> On Wed, Apr 8, 2020 at 4:55 PM Floris Bruynooghe <flub at devork.be> wrote:
>
>> Hi Harry,
>>
>> To the best of my knowledge you stumbled into a hard and dark corner of
>> pytest.  IIRC previous attempts at improving this have not gone too
>> well.  But like this always goes, it sounds like you've set yourself up
>> to be the expert now and are in a great position to clean this up and
>> make it work nicely for people.  ;)
>>
>> Cheers,
>> Floris
>>
>> On Tue 07 Apr 2020 at 19:26 +0100, Harry Percival wrote:
>>
>> > cf discussion here https://github.com/pytest-dev/pytest/issues/162
>> >
>> > I'm working on pytest-icdiff, trying to get it to print out well
>> optimised
>> > messages for different terminal sizes, and it's hard.
>> >
>> > when i'm running tests using runpytest, and I _think_ in real life too,
>> > config.get_terminal_writer().fullwidth *inside the hook* is returning
>> > incorrect values: resizing the terminal i'm using to run the tests has
>> no
>> > effect on the value i get from it.  and when I use that value irl, real
>> > test output does not adjust correctly to the terminal size
>> >
>> > but calling py.io.TerminalWriter().fullwidth _outside_ the hook, eg at
>> > module level, _does_ give me readings that look right.  but testing
>> that
>> > is hard.
>> >
>> > intriguingly, if I do testdir.monkeypatch.setenv('COLUMNS', '50'), then
>> the
>> > fullwdith *inside* the hook varies.  but that's no use to me, since IRL
>> > that value doesn't work.
>> >
>> > so my question is: a) does anyone know of any good examples of
>> assertrepr
>> > plugins that adjust dynamically to terminal width, and b) what's a good
>> way
>> > of writing tests for that?
>> >
>> > here's the repo fwiw
>> >
>> https://github.com/hjwp/pytest-icdiff/blob/master/tests/test_pytest_icdiff.py
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