Ciao Ivo,
enriching the testbed is definitely possible (and I have a vested interest in that happening, being a testing fanatic and one co-author of a prehistoric version of the testbed). However the GAE SDK, while available on github, is not developed there, but rather internally (other, newer open-source Google programs *are* developed on github -- just not that one, sigh).
If you send your patch to me privately I'll push it through internal channels. If you need my work email, you'll find it in the PDFs for any of my testing-related tech talks, such as
http://www.aleax.it/yt_pydi.pdf (just happen to be top hit on my web search for that:-). (Italiano, my first language, and Français, my second one, also fine for private communication, though English, my third one, is the only language supported on these forums).
Alex