Autotest depends on the rules you use.

Find autotest/discovery.rb for your project to see something like:

    Autotest.add_discovery { "Rspec2" }
    Autotest.add_discovery { "Rails" }
    # both of the frameworks have their predefined rulesets

No one prevents you from adding your own discovery rules.

Also you're looking for autotest-fsevent if you're using a mac. Probably something similar exists for linux.