DOC: More specific test instructions.

README_SETUP.md

@@ -103,7 +103,10 @@ like this, check out the "Authentication" section in the [configuration document
 Now would be a good time to continue with the [tutorials](tutorials/index).
 
 ## Run Unit Tests
-tox
+
+- Run all tests: `tox` or `make unittest`
+- Run a specific test file: e.g. `tox -- unittests/test_schema.py`
+- Run a specific test function: e.g. `tox -- unittests/test_schema.py::test_config_files`
 
 ## Documentation ##