CONTRIBUTING.md could/should include advice to run tests (and pre-commit)

[danielsparing]

Is your feature request related to a problem? Please describe.
It is unclear to a new contributor whether any linting or tests should be run on the code before submitting for pull request.
Describe the solution you'd like
Given that there is a pre-commit config file and a test directory, probably the advice in CONTRIBUTING.md should be to run these two before submitting -- and running tests might need some further guidance around the testing suite used.

Plus there could be a mention about any CI workflows on GitHub that should succeed before a merge could be considered.