Integrate go cover into test executions

[marpaia]

Go has a tool which will track how much of a codebase is tested. Perhaps we can use this to ensure we don't start adding untested code?

https://godoc.org/golang.org/x/tools/cmd/cover

[zwass]

love it

[marpaia]

The tests show go cover information. One day, we should enforce 100% test coverage, but I think this issue is sufficiently closed for now.