There aren't many unit test for `SlackClient` and with https://github.com/DonDebonair/slack-machine/pull/1194 there is even less test coverage. This issue is to track adding unit test coverage. Ideas: * I want to use [vcrpy][1] so that we have real-world interactions that we can re-run repeatedly and fast. [1]: https://github.com/kevin1024/vcrpy
