Tests! Tests everywhere!

[DanielOaks]

Testing this is difficult. Quite difficult.

Perhaps integration tests could work similarly to gIRC-go, i.e. setting up a fake client and ensuring the responses are correct?

There should be a bunch of stuff in here that we can verify with ordinary tests though. Ensuring mode changes are built into correct strings, mode change strings are decided properly, etc etc etc.

[slingamn]

Subsumed by #427