I've worked on extending the Hypothesis property-based test for PyPy's garbage collector to exercise more of the GC's features.
I've now added tests for pinning (temporarily ask the GC to not move a string around in memory, to be able to pass it to a C function) and for Python's id function (takes an object and returns an integer that stays the same over the lifetime of the object).
Of course it immediately found more mem corruption bugs :-(. they're now fixed.
lilyf