[35] Support async/await fixtures

[altendky]

Redo of #36 but straight off of master

WIP for:

• Actual timeout for concurrent teardown test
  • Add timeout to testdir.run() pytest#4073
  • Handled the timeout internally in b0b623e
• Consideration of requiring decorator for async fixtures
  • I'm tempted to say we should do this. What with explicit being good and all.
• Self review with a fresh brain
• Proper ordering of fixture setup and teardown including inter-fixture dependencies
  • Proper ordering of async fixture setup and teardown including inter-fixture dependencies #57

[altendky]

Does not support yield in the async fixture yet. Though I'm just all around skeptical I've got this right anyways...

[altendky]

@schmir and @vtitor, any opinions on this? Concerns? One consideration that was suggested was to actually require an explicit mark of some sort for pytest-twisted to manage the async def instead of just consuming them all. I believe it was pytest-trio that was setup this way.

[altendky]

Also, pytest-asyncio pytest-trio (see below) requires async fixtures to be function scoped. I believe my present implementation should have that restriction as well (both in code and documentation).

[meejah]

:LGTM:
(caveat: I've just read the code, not tried it myself yet..)

[meejah]

@altendky Hmm, why does asyncio insist on function-scoped async fixtures...?

[altendky]

@meejah, my apologies. It was Trio that only has function scoped fixtures. They have no global reactor and start a new one (so to speak) for each test. It seems that asyncio does support all fixture scopes.

https://github.com/pytest-dev/pytest-asyncio#async-fixtures

[altendky]

It doesn't seem like async fixture scope needs to be be restricted to just 'function'. Perhaps shifting to using pyest_fixture_setup() would be part of eliminating the restriction.

[meejah]

Okay, yeah from my perspective at least having all scopes would be best :)

I wonder if this should ape asyncio with a reactor fixture, too..? I certainly have made reactor fixtures for several Twisted + pytest things .. but I don't know how/if these would work with some pytest-twisted-provided reactor fixture. e.g. one reason I had my own reactor fixture was to parametrize it on two different reactors (or, e.g., to ensure a particular reactor was being selected).

I guess I'm asking: if pytest-twisted provided a reactor fixture, can a conftest.py that I write override that?

[altendky]

As I recall, pytest-twisted tries to setup the global reactor asap and leave it running throughout. I don't know what it would take to move away from the global reactor.

#16 (comment)

[meejah]

As I recall, pytest-twisted tries to setup the global reactor asap and leave it running throughout. I don't know what it would take to move away from the global reactor.

Ah, okay, ignore that thought for this PR, then.