[otikik]

> the whole problem gets exacerbated by unit testing, where `list_of_resources` can be a MagicMock, and therefore `if not list_of_resources` will never trigger

Not a python or javascript programmer, but that alone already points at using `len` as a better (more testable) solution.

In my limited understanding of python, there's no type-checker that will shout if someone in another team changes method_a() to sometimes return a `None` or `False` in addition to a List. So even if in python empty lists are falsy, the code will be a bit more robust if it doesn't rely on that feature to begin with. The code will error on the if instead of continuing and trying to use a `None` in a place where a list is expected later on.

Disclaimer: I work with a language with only two falsy values (nil and false), so I might be biased