Testing Asynchronous OTP

22. defmodule RollingAverage do use GenServer def start_link(limit), do: # ... def add(pid, n), do: # ... 
 def average(pid), do: # ... end
25. test "add/2" do {:ok, pid} = RollingAverage.start_link() RollingAverage.add(pid, 3) # Now what? end
27. test "add/2 and average/1" do {:ok, pid} = RollingAverage.start_link(2) RollingAverage.add(pid, 3) RollingAverage.add(pid, 4) assert RollingAverage.average(pid) == 3.5 RollingAverage.add(pid, 5) assert RollingAverage.average(pid) == 4.5 end
29. defmodule RollingList do def new(limit), do: {limit, []} def add({limit, list}, n), do: # ... def average({_limit, list}), do: # ... end
30. test "add/2" do rolling_list = RollingList.new(2) assert RollingList.add(rolling_list, 3) == {_limit = 2, [3]} end
32. test "add/2" do {:ok, pid} = RollingAverage.start_link(2) RollingAverage.add(pid, 3) state = :sys.get_state(pid) assert state == {_limit = 2, [3]} end
35. test "add/2 and average/1" do {:ok, pid} = start_supervised( {RollingAverage, _limit = 2} ) # Same as before end
37. def background_work do Task.start(fn -> do_something() end) end
40. def background_work(parent, ref) do Task.start(fn -> do_something() send(parent, {ref, :done}) end) end
41. test "background_work/0" do ref = make_ref() background_work(self(), ref) assert_receive {^ref, :done} end
43. def background_work do Task.start(fn -> :ok = twitter_module.post() end) end
44. test "background_work/0" do parent = self() ref = make_ref() Mox.expect(TwitterMock, :post, fn -> send(parent, ref) :ok end) background_work() assert_receive ^ref end
46. defmodule WeatherChecker do use GenServer def init(_) do :timer.send_interval(5000, self(), :tick) end def handle_info(:tick, _) do check_weather() end end
47. test "checking weather periodically" do {:ok, _pid} = WeatherChecker.start_link() Process.sleep(5000 * 1.5) assert weather_checked?() end
49. defmodule WeatherChecker do use GenServer def init(_) do :timer.send_interval(5000, self(), :tick) end def tick(pid), do: send(pid, :tick) def handle_info(:tick, _) do check_weather() end end
50. test "checking weather periodically" do {:ok, pid} = WeatherChecker.start_link() WeatherChecker.tick(pid) assert weather_checked?() end
51. defmodule WeatherChecker do use GenServer def init(:interval) do :timer.send_interval(5000, self(), :tick) end def init(:manual) do # No send_interval end end
53. @mix_env Mix.env() def start(_type, _args) do Supervisor.start_link(children(@mix_env), ...) end defp children(:test), do: [...] defp children(_env), do: [WeatherChecker | ...]
58. test "cleanup after crashes" do Process.flag(:trap_exit, true) {:ok, pid} = start_supervised(MyServer) Process.exit(pid, :kill) assert cleanup_successful?() end