Add rules on testing to github PR template.

[fisx]

This is a follow-up on our discussion on unit testing in the last C&D.

I propose to add testing check boxes to the checklist below. Like with the changelog item, you can try to convince the reviewer that you didn't check them. But it will at least keep it in front of our minds during PR creation that we want unit tests.

No need for a changelog entry. :)

Checklist

• [ ] Add a new entry in an appropriate subdirectory of changelog.d
• [x] Read and follow the PR guidelines

[fisx]

it'll remind us, though. and motivates us to change that.

[battermann]

Realistically, most of our code can't be covered by unit tests. Having a box to tick isn't going to change that.

Not sure if it's most but still a lot, but I agree. A box that can't be ticked very frequently does not provide much value. Regarding integration tests, AFAICT everyone is writing them already, and reviewers usually point out when missing.