Russell Owen, I'll make the fixes, in the meantime:

For #1, feel free to remove that metadata; that was missed from previous changes to the template.

For #2, they are different lines, but if you're only developing on Python 3.8 you don't need the backport package ( importlib_metadata ).

For #3, again feel free to remove the init_routes from }}{{_all_.

Another thing: are the __init__.py files the tests directory needed? I see them at every level (3 levels, 4 files). I'm guessing they are there so tests can find the handlers. But I thought such files aren't needed in Python 3.

That decision was based on feedback from Russ Allbery, who pointed out that it can be beneficial to keep test helpers in the tests "package" rather than adding them to the application or relying on fixtures from conftest.py exclusively. If you don't want this feature, feel free to delete those _init_.py files. Your tests will work without them. I don't think be taking them out of the template, though.

Finally: the newly created files could not be committed because isort said some imports were out of order.
I used the package name "owl" in case that makes a difference.

You can run tox -e lint and commit the results. See https://safir.lsst.io/set-up-from-template.html#format-code-with-black

The __init__.py files should not be needed with Python 3 in order to run code that is in the tests directory. Such files were needed in Python 2 but not in Python 3 in order to make a directory into a package. Russ Allbery: I understand you requested these files? If so, have you tried running the tests without them?

I've fixed the extra _all_ statements and the import order issue.

The __init__.py files in the tests directory are required with Python 3. If they are not present, you cannot use the same test name in multiple directories. The errors that happen in this case are quite obscure and can be difficult to debug, so ensuring that __init__.py files always exist saves a lot of hassle. (FWIW, this was also Guido's recommendation internally at Dropbox when he was providing guidance on our Python layout: always put a __init__.py file in any directory containing Python source to avoid a lot of weird edge cases.)