I've been doing this by running our test suite in an environment similar to the original Python 2.7 geminidev environment that our install instructions required, by updated to Python 3.5.6 (and with ...

usage: cythonize [-h] [-X NAME=VALUE,...] [-E NAME=VALUE,...] [-s NAME=VALUE] [-2] [-3] [--3str] [-+] [-a] [--annotate-fullc] [-x PATTERN] [-b] [-i] [-j N] [-f] [-q ...