Receive from Task.start_link?

Task.start* is for things where you don’t care about the return.

Are you testing the function return, or function side effects?

Also note that start_link will cause your processes to be linked, so be sure you’re ok with the user process dying resulting in the task being cancelled, potentially in a strange place. Otherwise, use Task.Supervisor.

I want to test the function output… mabye side effects too. This is for telemetry event handler - I want to know my code has executed.

You can create a simple wrapper module that depends on your mix environment to invoke the function (by call Kernel.apply/3 in test env), or to call Task.start_link (in prod env). Such that when running unit test, you can assert the result of do_work().

For example:

defmodule Hello.TaskWrapper do
   def start_link(module, func, args) do
    if Mix.env() == :test do
      apply(module, func, args)
    else
      Task.start_link(module, func, args)
    end
  end
end

Then in your code, you can use it like

arguments = []
Hello.TaskWrapper.start_link(__MODULE__, :do_work, arguments)