Mock out VCS/go get in order to improve testing speed

Is your feature request related to a problem? Please describe. During office hours, we discussed testing athens, and it seemed like one issue is that we have to actually call out to somewhere public to run tests. This isn't ideal for several reasons.

Describe the solution you'd like Ideally, this would just be a module.Fetcher implemented against a set of local filesystem objects

Describe alternatives you've considered None considered

Additional context Add any other context or screenshots about the feature request here.