add link to pytest config in running tests section

Author: lundybernard

docs/pages/principles/testing.md

@@ -395,9 +395,16 @@ total = numeric_sum(some_numeric_values)
 
 We recommend using Pytest for running tests in your development environments. To
 run unit tests in your source folder, from your package root, use
-`pytest {path/to/source}`. To run tests from an installed package (outside of
+`pytest {path/to/source}`.
+To run tests from an installed package (outside of
 your source repository), use `pytest --pyargs {package name}`.
 
+You can set the default test path in `pyproject.toml`, see:
+[Configuring pytest]({% link pages/tutorials/test.md %}#configuring-pytest)
+
+We recommend configuring pytest to run ONLY your fastest, least demanding test suite by default.
+
+
 #### Mocking and Patching to Isolate the code under test
 
 When the unit you are testing touches any external unit (usually something you