Elixir Deadlock, don't ever try to the same thing.

giveaway_manager.ex

defmodule TwitchSniper.GiveawayManager do
  use GenServer
  require Logger

  def start_link do
    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
  end

  def new_giveaway(item) do
    GenServer.cast(__MODULE__, {:new_item, item})
  end

  def get_first do
    GenServer.call(__MODULE__, {:get_first} )
  end

  def cycle do
    GenServer.call(__MODULE__, {:cycle} )
  end

  def start_cycling do
    Process.send_after(__MODULE__, {:time_trigger} , get_first.delay)
  end

  def start_cycling(delay) do
    Process.send_after(__MODULE__, { :time_trigger }, delay)
  end

  ##ServerSide Callback
  def init(:ok) do
    {:ok, :queue.new }
  end

  def handle_call({:get_first}, _from, state) do
    {:reply, :queue.get(state) , state}
  end

  def handle_call({ :cycle }, _from, state) do
    { {_,_}, new_queue} = :queue.out(state)
    new_item = :queue.get(new_queue)
    IO.inspect "New first item delay #{new_item.delay}"
    start_cycling(new_item.delay)
    {:reply, new_item, new_queue }
  end

  def handle_cast({:new_item, giveaway}, state) do
    {:noreply, :queue.in(giveaway, state)}
  end

  def handle_info({:time_trigger}, _state)do
    Logger.info "Starting cycle"
    cycle
  end

  def handle_info( message, _) do
    Logger.error message
  end

  # def terminate(_reason, _state) do
  #   flush
  # end

end

test.exs

defmodule TwitchSniper.GiveawayManagerTest do
  use ExUnit.Case

  alias TwitchSniper.Giveaway
  alias TwitchSniper.GiveawayManager

  test "Add 2 giveaways and cycle them" do
    giveaway_one = %Giveaway{organiser: "Asshole", product: "A very pc Game", delay: 200}
    giveaway_two = %Giveaway{organiser: "Not an asshole", product: "A Console", delay: 200}

    GiveawayManager.new_giveaway(giveaway_one)
    GiveawayManager.new_giveaway(giveaway_two)

    assert GiveawayManager.get_first == giveaway_one

    GiveawayManager.start_cycling
    :timer.sleep(giveaway_one.delay + 10) 

    assert GiveawayManager.get_first == giveaway_two
  end

end