Extend tox.ini with {posargs} in poetry-pytest invocation

This allows limiting the scope of the test run, which can save much time.

Run all tests:
    tox
Run all tests in one file in all test environments:
    tox -- tests/test_api.py
Run one test in all test environments:
    tox -- tests/test_api.py::test_api
Run all tests in one test environment:
    tox -e py39
Run all tests in one file in one test environment:
    tox -e py39 -- tests/test_api.py
Run one test in one test environment:
    tox -e py39 -- tests/test_api.py::test_api

Author: chrisinmtown

tox.ini

@@ -1,3 +1,16 @@
+# Run all tests:
+#   tox
+# Run all tests in one file in all test environments:
+#   tox -- tests/test_api.py
+# Run one test in all test environments:
+#   tox -- tests/test_api.py::test_api
+# Run all tests in one test environment:
+#   tox -e py39
+# Run all tests in one file in one test environment:
+#   tox -e py39 -- tests/test_api.py
+# Run one test in one test environment:
+#   tox -e py39 -- tests/test_api.py::test_api
+
 [flake8]
 exclude=connexion/__init__.py
 rst-roles=class,mod,obj
@@ -34,7 +47,7 @@ commands=
     poetry lock
     poetry install --all-extras --with tests
     poetry show
-    poetry run python -m pytest tests --cov connexion --cov-report term-missing
+    poetry run python -m pytest tests --cov connexion --cov-report term-missing {posargs}
     min: mv -f pyproject.toml.bak pyproject.toml
 
 [testenv:pre-commit]