A mockable Task module for elixir (with mox)

mokable_task.ex

# lib/my_project/task.ex
defmodule MyProject.Task do
  @moduledoc """
  TODO: run async task on tests will not work, with unpredictable side effects
  """

  @adapter Keyword.get(
             Application.compile_env(:my_project, __MODULE__, []),
             :adapter,
             Task
           )

  @callback async(term()) :: term()

  defdelegate async(func), to: @adapter
end

# configs/test.exs
config :my_project, MyProject.Task
  adapter: MyProject.Task.MockAdapter

# tests/support/mocks.ex
Mox.defmock(MyProject.Task.MockAdapter, for: MyProject.Task)

# test/lib/my_project/task_test.exs
test "spawn a task" do
  MyProject.Task.MockAdapter |> expect(:async, 1, fn fun -> fun.() end)

  assert capture_log(fn ->
           MyProject.Task.async(fn ->
             Logger.error("Houston, we have a problem")
           end)
         end) =~ "Houston, we have a problem"
end