FIX: Make testing slightly cleaner

This does not fix the problems in `master`, but it should make them easier to diagnose. Ready for review/merge from my end. 
I'm assuming that when we fix the 2.6/2.7 builds, these will also be fixed. If it doesn't fix them, then we should just put a single `raise SkipTest` in the `TestingCanvas` call for simplicity anyway.