exactly once.  But the test code can't know that, as the number of times
__cmp__ is called depends on internal details of the dict implementation.
This is especially nasty because the __hash__ method returns the address
of the class object, so the hash codes seen by the dict can vary across
runs, causing the dict to use a different probe order across runs.  I
just happened to see this test fail about 1 run in 7 today, but only
under a release build and when passing -O to Python.  So, changed the test
to be predictable across runs.