Fix it so py.test by itself doesn't crash

Change setup.cfg so that pytest only runs tests in the tests directory by default.

Attempting to run tests in the isolated_tests directory was causing a crash

Author: tleonhardt

setup.cfg

@@ -1,3 +1,7 @@
+[tool:pytest]
+testpaths =
+    tests
+
 [flake8]
 exclude = .git,.idea,.pytest_cache,.tox,.nox,.venv,.vscode,build,cmd2.egg-info,dist,htmlcov,__pycache__,*.egg
 max-line-length = 127