gen_reset/test/gen_reset_tracker_test.exs

defmodule GenReset.TrackerTest do
  use ExUnit.Case

  setup do
    GenServer.call(GenReset.Tracker, :reset)
    :ok
  end

  test "adding pids" do
    assert GenReset.Tracker.add(self()) == :ok
    assert GenReset.Tracker.pids == [self()]
  end

  test "removing existing pid" do
    assert GenReset.Tracker.add(self()) == :ok
    assert GenReset.Tracker.pids == [self()]
    assert GenReset.Tracker.remove(self()) == :ok
    assert GenReset.Tracker.pids == []

  end

  test "dead pid is automatically removed" do
    pid = Process.spawn(fn ->
      receive do
        _ -> :ok
      end
     end, [])
    GenReset.Tracker.add(pid)
    assert GenReset.Tracker.pids == [pid]
    Process.exit(pid, :kill)
    TimeHelper.wait_until(fn ->
      assert GenReset.Tracker.pids == []
    end)
   end
end

defmodule TimeHelper do

  def wait_until(fun), do: wait_until(500, fun)

  def wait_until(0, fun), do: fun.()

  def wait_until(timeout, fun) do
    try do
      fun.()
    rescue
      ExUnit.AssertionError ->
        :timer.sleep(10)
        wait_until(max(0, timeout - 10), fun)
    end
  end

end