I'm having trouble finding a word which fits. I did a google search for testudineousness and testudinateness, but sadly had no hits.
It sounds like you have tried to apply the same rule as seen in words like "bovine", "feline", etc, but with the latin for the tortoise family, which is "testudo". I'd expect the word generated from this process to be "testudine", not the words you list.
This does appear to exist as a word: http://www.thefreedictionary.com/Testudine
Strictly speaking this means "of the order Testudo", but, like "feline" or "bovine", and many other similar examples, the meaning could cross over into an adjective used to describe characteristics of other things (eg people).
So, if you were jogging with someone, and you were much faster than them, you could say "Your testudine pace is way too slow for me!". Whether they would know what you were talking about is a different matter.