At a meetup the difficulty of testing several processes was discussed, and I wondered if registries could be used to make named processes more async-friendly for tests. This is a proof of concept for that idea.
Our app has two GenServers: Alpha and Bravo. Bravo typically makes calls to the Alpha server, but for our tests we want it to call our mock server AlphaMock.
We could pass in a pid or a test-specific name for our AlphaMock server, but if we had a lot of other servers to call instead of one, that could add a lot more clutter to our Bravo module. Instead this example takes advantage of OTP's {:via, module, name} process names (see Using in :via) to hopefully simplify it all.
- Alpha
Simple incrementing GenServer - AlphaMock
Mock of Alpha In this case it extends Alpha's behavior, but your mocking should be whatever's best for your tests. - Bravo
GenServer that depends on Alpha Takes a registry option, used to determine name of Alpha server - BravoTest
Starts up Registry, AlphaMock, and Bravo; tests against Bravo Registers AlphaMock server in registry as Alpha and passes registry to Bravo on startup
It's not as simple or pretty as I'd like, but it's an interesting idea. Maybe there's a way to move some of the registry injection code out of Bravo into its own reusable module.