Hi all,

I have a simple GenServer that performs some initialisation on start. That initialisation process involves making some calls to an HTTP API. I have delegated the HTTP communications to a lower level module, which I then mock using Mox. All well and good.

The GenServer is in my supervision tree in a vanilla sort of way so it gets started every time I run mix test. That would be fine except the GenServer starts making calls to my mock before I’ve had a chance to specify what the response should be, and mox raises a Mox.UnexpectedCallError.

So my question is; what’s the most idiomatic way of testing this? Options I’ve considered:

• Preventing applications from being manually started by using mix test --no-start and then manually starting the pieces I need. This is fine but the auto-start behaviour is working nicely elsewhere so would add more work.
• Selectively changing which processes are started depending on environment. Again this works fine.

Something tells me there is a better way. Thanks for any help!