Add test tools based on the new type structure

[beorn7]

Once #223 is done, we can make use of it for better testing tools (like mocking helpers for the various interfaces we end up with).

[marco-m]

Hello @beorn7 , I stumbled upon this ticket investigating about testability of Prometheus instrumentation. Are there any news/plans related to this ticket and #223 ? Thanks.

[beorn7]

This is all planned for the v0.10 (soon to be renamed v2) milestone. I still need to finalize the grand design of it to enable detailed work like this one.

Have you looked at https://godoc.org/github.com/prometheus/client_golang/prometheus/testutil ? It should satisfy most of the current needs.

[marco-m]

I will look at testutil, thanks for the prompt answer!