This seems pretty messy :(.  Elsewhere in rspec-mocks we test this kind of stuff by showing the effects that `reset` has.  (Knowing that rspec-core calls that after each example).  It helps focus the example on the rspec-mocks APIs that come into play rather than the rspec-core ones.

Alternately, if you want to do this kind of thing (where you define example groups and examples from within an example and then run them), maybe we should port rspec-core's sandboxing logic to rspec-support so you can use it here?