Time spent making undergraduates use git is time that could be spent teaching them long-term, fundamental skills.
there's no better way to learn something difficult than to learn it when you're young
Hmm, define 'young'. I'm in my late 20s and I find it easier to learn new things more than ever - including things I failed to learn in my teens and early 20s. Maybe I'm just a late bloomer, and it took me a while to "learn how to learn". But maybe I'm still young in the eyes of someone who has been using vi for 30 years (:
Testing ect is usually covered in all intro classes (assert libraries) or industry type testing like JUnit by a software engineering elective typically taught in Java
Just because one of gits key abstractions is based on a kind of graph, I don't think it follows that knowing graph theory means you know git. I mean LISP is based on a graph structure as well but plenty of people find that confusing.
You have to do programming assignments anyway. Why wouldn't you require students to learn and use the latest source code control tools while they're doing their development?
Teach students to write tests, use source code control, utilize continuous integration, etc.
Although the specific tools, languages, and approaches will evolve in the coming years - none of the above are going away soon.