standardizing test execution

[edublancas]

Contributors sometimes have issues running tests locally because they must pass special flags they're unaware of. For example, to run JupySQL's unit tests, you need to run the following:

pytest --durations-min=5 --ignore=src/tests/integration

However, many contributors attempt to run:

pytest

Which will fail since this will run all tests (including integration tests, which contributors often don't want to run)

I investigated a few options and concluded that our best bet is to ensure that this works on all projects:

pytest

And document other alternatives (e.g., how to run integration tests)

see: ploomber/jupysql#335