.. note::

   $ find sphinx tests LICENSE doc/conf.py -type f -exec sed -i '' -e 's/2007\-20../2007-2021/' {} \;
   $ git co sphinx/locale/**/*.js sphinx/templates/epub3/mimetype

Run `pyupgrade --py3-only --keep-percent-format` to refine our code.

Note:  --keep-percent-format is required to keep translations available.

Allows relative imports.

Keep imports alphabetically sorted and their order homogeneous across
Python source files.

The isort project has more feature and is more active than the
flake8-import-order plugin.

Most issues caught were simply import ordering from the same module.
Where imports were purposefully placed out of order, tag with
isort:skip.

Makes the test more realistic by issuing an HTTP request.
Reduces coupling between test and the code under test.

The `http_server` helper was factored out into a new tests.utils module.