test: Fix coverage reporting

By adding the current working directory to the `sys.path`.

Run via `python -m pytest` (not `py.test`) so the working directory
is on `sys.path`, and coverage measures the local `injector/`
rather than the copy installed in site-packages. Otherwise coverage
reports 0%.

See pytest-dev/pytest-cov#98

Author: davidparsson

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
         pip install .
     - name: Run tests
       run: |
-        py.test -vv --cov=injector --cov-branch --cov-report html --cov-report term
+        python -m pytest -vv --cov=injector --cov-branch --cov-report html --cov-report term
         if which mypy; then mypy injector ; fi
         if which black; then black --check . ; fi
         check-manifest