defmodule TcpTest do
  use ExUnit.Case
  alias Modbus.Tcp

  #http://www.tahapaksu.com/crc/
  #https://www.lammertbies.nl/comm/info/crc-calculation.html
  test "wrap test" do
    p  0, <<>>, <<0,0,0,0,0,0>>
    p  1, <<0>>, <<0,1,0,0,0,1,0>>
    p  2, <<0,1>>, <<0,2,0,0,0,2,0,1>>
    p  3, <<0,1,2>>, <<0,3,0,0,0,3,0,1,2>>
    p  4, <<0,1,2,3>>, <<0,4,0,0,0,4,0,1,2,3>>
  end

  defp p(transid, payload, packet) do
    assert packet == payload |> Tcp.wrap(transid)
    assert {payload, transid} == packet |> Tcp.unwrap
  end

end