Test to check there are no duplicate smart answers/flows

The smart-answers part of this story: https://www.agileplannerapp.com/boards/105200/cards/6367

Bit of a strange commit since you can't automatically test a test. Feel free to pull down and temporarily create a duplicate flow if you want to see it work!
As someone still learning ruby nuance the use `send` was a bit confusing. Agree there's no reason not to make `available_flows` public - we're effectively using it like it is, and it'll make the code here a bit simpler.

Other than that small change this is ready to good to merge.