Passing a custom clock to the executor in tests

[fjarri]

Things to check first

• I have searched the existing issues and didn't find my feature already requested there

Feature description

pytest-trio has a very useful feature of supporting custom clocks that are passed to trio.run() when running a test (see https://pytest-trio.readthedocs.io/en/stable/reference.html#mock_clock, basically it looks through fixtures to see if something derives from trio.abc.Clock). I couldn't find a way to do this for anyio tests. Is it something that's impossible by design, or just hasn't been implemented yet?

Use case

Reducing test runtime for code that relies on some internal waiting times, e.g. running recurrent tasks.

[agronholm]

The problem is that asyncio doesn't support this.

[fjarri]

I see, that's what I suspected when I said "impossible by design" :) There is some hacky library to do that: https://github.com/nolar/looptime, but I'm not sure how well it works.