I've run the black code formatting tool against everything:
black tests datasette setup.py
I also added a new unit test, in tests/test_black.py, which will fail if the code does not
conform to black's exacting standards.
This unit test only runs on Python 3.6 or higher, because black itself doesn't run on 3.5.
The extra_css_urls and extra_js_urls hooks now take additional optional
parameters.
Also refactored them out of the Datasette class and into RenderMixin.
Plus improved plugin documentation to explicitly list parameters.
https://github.com/pytest-dev/pytest/issues/1875 made it impossible to declare
a function as a fixture multiple times, which we were doing across different
modules. The fix was to move our @pytest.fixture calls into decorators in the
tests/fixtures.py module.
Simon Willison