There is currently a test that [sets different versions of the package and runs go code to make sure the output is correct](https://github.com/VividCortex/johnny-deps/blob/master/test/installs_correct_versions_test.sh) without deleting anything nor setting a different GOPATH.

Have you tried to run this locally? Tests shouldn't only be able to be run on the CI server, relying on this is a severe limitation.