Virtual time for GenServer and :gen_statem: test time-dependent processes by advancing a clock a test owns, instead of sleeping through the timeline.

This package is the clock and the OTP wrappers, and nothing else. The rest of the library is published separately, with the same module names, so what you need is a dependency rather than a rewrite:

mix virtual_time.doctor reads a project and says which of them a missing module needs.

Quick Example

# Define a time-dependent GenServer
defmodule MyServer do
  use VirtualTimeGenServer

  def init(_) do
    VirtualTimeGenServer.send_after(self(), :tick, 1000)
    {:ok, %{count: 0}}
  end

  def handle_info(:tick, state) do
    {:noreply, %{state | count: state.count + 1}}
  end
end

# Test it with virtual time (instant!)
test "ticks 10 times in 10 seconds" do
  {:ok, clock} = VirtualClock.start_link()
  VirtualTimeGenServer.set_virtual_clock(clock)

  {:ok, server} = MyServer.start_link(nil)
  VirtualClock.advance(clock, 10_000)  # Instant!

  assert get_count(server) == 10
end

Modules

• VirtualClock - the virtual timeline and its scheduled events
• VirtualTimeGenServer - a GenServer that schedules on that timeline
• VirtualTimeGenStateMachine - the same for :gen_statem
• VirtualTimeGenServer.Instrumentation - the port for measuring a server
• VirtualTimeGenServer.Doctor - reports modules a project is missing

See the README for examples and the design docs for the clock.