Pylint's `bad-classmethod-argument` is disabled for each definition
to avoid rewriting the method bodies just to rename `self` → `cls`.
This can be done gradually, as the setUpTestData methods are modified
along the way.
Anywhere we have a user object, we can easily get the user ID in the
caller, and this will allow us more flexibility in the future to
implement optimizations that involve knowing a user ID without querying
the database for the user object.