Do tests on Git repositories properly

[hectorj]

We need to do tests on actual Git repositories and their sub-modules

Problems :

• Current solution (cloning from Github) makes the tests impossible to run without an internet connection, and potentially slow.
• Git doesn't let me just commit a repository inside a repository (only as a sub-module, but that's not the same thing)
• The vendor test takes a remote URL from the package in the GOPATH, and fetches it as a sub-module... That's messed up as I do not control what remote is used in the GOPATH. (could be "fixed" by setting my own GOPATH for the test with a pre-defined repo inside...)

As a temporary solution, I'm gonna zip up the test repo and skip the vendor tests...

Any idea is welcome

[hectorj]

After the make-over ( #6 ), new partial solution :
Do not unit tests the git commands themselves, mock them thanks to https://github.com/tsuru/commandmocker

[hectorj]

Replaced commandmocker by having a GitService interface, with both a real service and a stub that satisfies it