That is not possible to do locally, `go get` will only bring stuff in from remotely hosted repositories, not local ones.

That gpm works and tests pass can be seen in [Travis](https://travis-ci.org/pote/gpm), lots of other formulae - like [ruby](https://github.com/Homebrew/homebrew/blob/master/Library/Formula/ruby.rb) and [ocaml](https://github.com/Homebrew/homebrew/blob/master/Library/Formula/objective-caml.rb)
 just to name examples - don't even have tests. Is the problem here that the test is not good enough and we could just remove it?

The only way to test this meaningfully would be to use the `testpath` to create a Godeps file, point GOPATH to that folder and install some package there, but I would have to cross my fingers and hope Go is already installed in their systems since I can't add Go as a dependency in the homebrew formula - every user has it installed outside of Homebrew, because the Go formula doesn't work - should the installation fail and ask the user to install Go outside of homebrew when this happens? I can do that.