So, in this case, I don't think PathHelpers needs to be a mixin, since it's not being mixed in anywhere. I don't like the semantics on Util, though, and would suggest a Berkshelf::ShellOut class that mimics the calling behavior of mixin-shellout: make an instance with a command to run, maybe set some env vars or tweak the object in some way, tell it to run the command, and check the response directly on the object.

The guts of shell_out look good, I just don't like them as quasi-statics.

If it's a pain to change, or if you really feel strongly that Util is the best place, I can live with it.