A behavior module for GenServers with virtual time support.

This module wraps GenServer and provides a send_after/3 function that can work with either real time (production) or virtual time (testing).

Example

defmodule MyTimedServer do
  use VirtualTimeGenServer

  def start_link(opts) do
    VirtualTimeGenServer.start_link(__MODULE__, :ok, opts)
  end

  @impl true
  def init(:ok) do
    # Schedule a tick every 1000ms
    schedule_tick()
    {:ok, %{count: 0}}
  end

  @impl true
  def handle_info(:tick, state) do
    new_count = state.count + 1
    schedule_tick()
    {:noreply, %{state | count: new_count}}
  end

  defp schedule_tick do
    VirtualTimeGenServer.send_after(self(), :tick, 1000)
  end
end

Testing with Virtual Time

test "server ticks correctly" do
  {:ok, clock} = VirtualClock.start_link()
  VirtualTimeGenServer.set_virtual_clock(clock)

  {:ok, server} = MyTimedServer.start_link([])

  # Advance virtual time by 5 seconds
  VirtualClock.advance(clock, 5000)

  # Server will have ticked 5 times
  assert get_count(server) == 5
end