Better documentation on testing socketmode client

[dnck]

Description

I'm struggling to test my socketmode client. Ideally, I want to mock the slack server, and send different events to my connected client. I found the current docs on testserver, but didn't quite understand how to get it all wired up and I ended up writing my own mock websocket server, which still isn't working 100% but I got further than using the testserver. Is there any better documentation on testing a socketmode client? Alternatively, can one of the maintainers talk to me in this thread, and help me make a contribution to documenting how to do so for the community benefit?