gen_reset/test/gen_reset_test.exs

defmodule GenResetTest do
  use ExUnit.Case

  test "resets state manually" do
  	{:ok, pid} = GenServer.start_link(Server, :fresh_state)
  	assert GenServer.call(pid, :state) == :fresh_state
  	GenServer.cast(pid, {:set, :foo})
  	assert GenServer.call(pid, :state) == :foo

  	send(pid, :"$gen_reset")
  	assert GenServer.call(pid, :state) == :fresh_state
  end
end