Testing asynchronous code in Elixir

Question

I want to test a function which is using Task.async

In order to make my test pass, I need to make it sleep for 100ms before assertions, otherwise the test p

Answer 1

Since the question is a bit vague, I will give the general answer here. The usual technique is to monitor the process and wait for the down message. Something like this:

task = Task.async(fn -> "foo" end)
ref  = Process.monitor(task.pid)
assert_receive {:DOWN, ^ref, :process, _, :normal}, 500

Some important things:

• The fifth element of the tuple is the exit reason. I am asserting the Task exit is :normal. Change that accordingly if you are expecting another exit.

• The second value in assert_receive is the timeout. 500 miliseconds sounds like a reasonable amount given you currently have a 100 ms sleep.