Add pytest hook

[dspechnikov]

I was surprised pytest hook is missing. Is there any reason not to have it?

pytest is popular so I think we should include. If that's okay, I'll start working on PR.

[dspechnikov]

Now that I'm tried to implement it, I guess I understand the reason. Is it because pre-commit can't use existing project environment and there is no way to install project dependencies other than copying them to additional_dependencies?

[asottile]

The main reasons:

1. tests are often slow, committing should be fast
2. It would have to be a system / script hook since you'd need repository specific dependencies installed (as you've noticed)

That said, if you wanted to do something like this, I've outlined a way to do that here

Also a fun bit of history, the original pre-commit used to run make test as a hook but was quickly removed due to (1.) above.