How do I use Req.Test stubs with Poolboy?`

Questions / Help
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1

I’m making HTTP requests from inside a Poolboy pool.

I’m having a hell of a time trying to use Req.Test stubs in ExUnit in an e2e workflow sort of test.

Typically the error I get is:

** (EXIT from #PID<0.1312.0>) an exception was raised:
         ** (RuntimeError) cannot find mock/stub MyApp.WorkerStatusRequest in process #PID<0.1318.0>

I know that I need to use Req.Test.allow, but getting my test process pid into the code where poolboy runs has proven a challenge.

I’ve gone as far as trying to do an if Application.get_env(:my_app, :env_name) == :test do ... sort of check, using an agent to store a parent pid, but that feels hacky, plus it doesn’t allow me to configure my mocks for each individual tests. The more I try the more tangled of a mess I seem to make.

I can’t help but think there must be an elegant solution here. Can anyone point me to any examples?

2

The mechanism described in Req.Test — req v0.5.15 is a sort of escape hatch I guess. Hope that helps!

1 Like
3

Are you writing the poolboy worker yourself? If so, you can set the :"$callers" in the process dictionary of the worker process, which is then used by the ownership mechanism in Req.Test.

def start_link(opts) do
  opts = Keyword.put_new(opts, :callers, Process.get(:"$callers", []))
  GenServer.start_link(__MODULE__, opts)
end

def init(opts) do
  {callers, opts} = Keyword.pop(opts, :callers)
  Process.put(:"$callers", callers)
  # ...
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4

I got this working! Took a few different tries and I had to have Claude help understand some of the errors but this was the approach that did it. Thank you Wojtek for an awesome library!

5

Thanks! I tried this but it didn’t work - $callers was always empty in my case although there could be a lot of reasons for that. I ended up going with the :telemetry based approach above.

6

Glad you got it to work!

I should have mentioned that setting callers would mean you wouldn’t need to allow the poolboy worker, but you might need to allow whatever is starting the worker (or pass the callers through whatever process that is) if that’s not happening in the test process itself.

1 Like