Consider renaming app.test.py to something else

[markdall]

This is mostly an FYI as I don't really want or expect you to change the name everywhere. Maybe you could add a note about it to the tutorial: VSCode's python test extensions don't handle dots in the filename per this. Test discovery fails, etc. If you rename it to app_test.py suddenly everything works as desired. They say this is intentional.

[mjhea0]

Thanks for the note. I'll make the change the next time I update the tutorial.

[mjhea0]

addressed in #63