testing fixtures

Need to create a system where the users can add data to a fixture that can be used in the testing of their app.
I think sphinx needs code blocks to look something like [this](https://github.com/praekelt/vumi-jssandbox-toolkit/blob/744dfcf6f989eb2b1ce7851205cc712d8f10706b/lib/tester/interactions.js#L212-L216)