mutex_test.exs

defmodule MutexTest do
  use ExUnit.Case, async: false
  doctest Mutex

  setup do
    Mutex.start
    on_exit fn ->
      Mutex.stop
    end
  end

  test "acquiring mutex" do
    assert Mutex.wait() == :ok
    Mutex.signal()
    assert Mutex.wait() == :ok
  end

  test "two processes test" do
    Mutex.wait()
    current = self()

    spawn(fn ->
      Process.sleep(1)
      value = Mutex.wait()
      send current, {:value_received, value}
    end)

    Mutex.signal()

    assert_receive {:value_received, :ok}
  end

    test "two processes test waiting for mutex" do
      Mutex.wait()
      current = self()

      spawn(fn ->
        value = Mutex.wait()
        send current, {:value_received, value}
      end)

      Process.sleep(1)
      Mutex.signal()

      assert_receive {:value_received, :ok}
    end


  test "other two processes test" do
      Mutex.wait()
      current = self()

      spawn(fn ->
        IO.inspect current
        IO.inspect self()
         case Mutex.signal() do
           :ok -> send current, {:value_received, :ok}
           _ -> :ok
         end
      end)
      Process.sleep(1)
      Mutex.signal()
      refute_receive {:value_received, :ok}
    end

    test "call wait twice in same process" do
      Mutex.wait()
      assert :ok = Mutex.wait()
    end

    test "call signal twice, should error" do
      Mutex.signal()
      assert :error = Mutex.signal()
    end

  test "when other process crashes" do
    spawn(fn ->
      :ok = Mutex.wait()
      exit(:funny_reason)
    end)

    Process.sleep(1)

    assert :ok = Mutex.wait()
  end
end