I discovered that the tests forPyNumber_ToBase only ever check one smallint value's conversions. The function description and implementation makes it quite clear that the intent is to support arbitrary ints, as would be expected for a function working with Pythonints. Tests should be added for some large negative and positive values in different bases to ensure that that's indeed the case and also for thePyNumber_Index conversion part.

(This has likely contributed to a bug in PyPy, namely that the function only accepts values in theint64_t range in PyPy:https://foss.heptapod.net/pypy/pypy/-/issues/3765)