Problem

FetcherFactory.New() starts a goroutine (go fetcher.run()) without providing a way to wait for that goroutine to finish on shutdown. Basically, Fetcher.run() crashes randomly on every shutdown. What kind of problem that can cause?

Solution

FetcherFactory.New() must return quit channel. When context is cancelled to initiate the shutdown, that channel must be closed eventually.

Then the wait for that shutdown signal must be implemented at every place where New() is called. Including TestFetcherFactory.