Explicitly clarify the difference between unit and system test files (#9419)
Explicitly clarify the difference between unit and system test files (#9419)

* Explicitly clarify the difference between unit and system test files

This aims to clarify for new contributors how to run the tests they've may have edited.

* There can be more than just `.test.ts`

For example: `.testvirtualenvs.ts`.

* Also mention functional tests

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