bpo-40129: Add fake number classes in test.support. by serhiy-storchaka · Pull Request #19262 · python/cpython

I agree with both points here.

When scanning through the PR on GitHub and seeing FakeInt(10.9), my first thought is that I don't know what that means without guessing, so I want to quickly find the FakeInt definition. That's harder when that definition is in another file. (And yes, if you have a decent editor open and set up properly, the definition should be just a click or keystroke away, but not everyone has that setup available all of the time.)

The problem could potentially be mitigated with a name that more clearly describes what the class is doing (HasDunderIntReturning(3.2)?), but as you can tell I'm having trouble coming up with a name that's going to be immediately unambiguous for people reading the code without also being unwieldy.