cli: unit tests for apollo command

[josephjclark]

I am not planning to do this before the apollo release, so here's some notes:

• Unit tests need to mock an apollo server. Not totally easy as it needs to be a websocket server.
• Don't test services, but test CLI behaviours. Like how to handle a { files } result
• Ideally I'd like tests against the echo service which can be easily reproduced with the actual CLI. So I can copy and paste the test name and just run it - a bit like how our integration tests work
• I don't want any integration tests on this right now