Pytest fail when warnings are raised

[adamltyson]

Closes #46

[niksirbi]

I'm a bit worried by this one. Should we document this somewhere (e.g. as a comment in pyproject.toml or in the README)? Perhaps we can link the pytest guide for capturing and controlling warnings that David mentioned. Otherwise, people will be perplexed and left without recourse when this first happens.

[adamltyson]

I thought about adding docs for this, but I realised that the docs don't cover pytest issues at all. If users use pytest, then they're on their own if any issues come up, not just this.

Realistically, I think we should tackle #36 and add some real docs about what each of the components do.

[niksirbi]

Realistically, I think we should tackle #36 and add some real docs about what each of the components do.

Agreed, but I'm afraid this will be a multi-day chunk of work. Anyhow, I'm going to approve and merge this one as is.