Documentation: how to run tests locally

[paskino]

I had to install pytest-cov and pytest-timeout to be able to run pytest on this repository.

Can this be documented. It is unclear how tests are running with CI on GHA.

Also, 2 tests are failing on my machine with master now.

[DanicaSTFC]

I was able to run all tests in one go but failed to run one test at a time.

Instructions to run one test at a time would be helpful too.

[lauramurgatroyd]

@paskino did you follow the instructions here https://github.com/TomographicImaging/eqt/blob/main/CONTRIBUTING.md to do pip install .[dev]? I did that and had no problem running pytest (other than the tests failing but that's a separate problem!)

[DanicaSTFC]

Tests are no longer failing.