CODEWITHSUNDEEP
erlangelixirintegration-testinggen-server
Jeremy Belolo
Jeremy Belolo

Reputation: 4539

Assert_receive to test Genserver message handlers?

I would like to be able to catch messages going to my GenServer's handle_info in tests, to check those are what I intend to.

1/ Is there a way to print somehow every message coming through? 2/ Using assert_receive is there a way to catch those messages? Should I set the assert_receive before or after the call to the external service that will result in the handle_info trigger? What syntax should I use?

I tried many combinations of assert_receive and I tried a receive do... to try and display messages getting in, with no success.

Upvotes: 0

Views: 831

Answers (1)

Aleksei Matiushkin
Aleksei Matiushkin

Reputation: 121000

Both ExUnit.Assertions.assert_receive/3 and ExUnit.Assertions.assert_received/2 do assert messages coming into the current process’ mailbox. The former is to be called either before or after the message was actually sent:

Asserts that a message matching pattern was or is going to be received within the timeout period, specified in milliseconds.

the latter is to be called after:

Asserts that a message matching pattern was received and is in the current process’ mailbox.

That said, both are unlikely a good fit to test the existing GenServer. Messages are to arrive at the GenServer’s messagebox, this functionality is provided by OTP and you should not test it. If you need to log messages, add a call to Logger.log/3 to the handle_info/2 and check the log actually happens with ExUnit.CaptureLog.capture_log/2. If it performs some action upon message arrival, test this action.

In general, you should test your code, not OTP.

Upvotes: 2

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