It seems like Guard and Autotest do about the same thing. Is there a
reason that they would be used together? Can they both be used against
Spork? If I’m using Rails 3.1, is one preferred over another?
They don’t really do the same thing.
Guard with guard-test doesn’t have an autotest test cycle.
Error, I am wrong 
Philippe Cantin wrote in post #1016167:
They don’t really do the same thing.
Guard with guard-test doesn’t have an autotest test cycle.
dwormuth wrote in post #1014058:
It seems like Guard and Autotest do about the same thing. Is there a
reason that they would be used together? Can they both be used against
Spork? If I’m using Rails 3.1, is one preferred over another?
Conceptually, I really like the looks of Guard. I have not yet used it
enough to recommend it outright. I don’t know of any specific issues,
just have worked with it enough yet.
Guard seems to be more modular, and I prefer its configuration options
over Autotest. For Spork support there is guard-spork. There is a pretty
extensive list of modules available for Guard.