Handling Phoenix Presence during testing

I have run into an issue while testing a simple Phoenix channel and using Phoenix.Presence.

It looks to me like the tests completes and the Presence process notices that a user has disconnected as a result. It then attempts to fetch the new user list but at that point the database connection has already been closed for that test. Is there any way to handle this sort of situation?

I tried calling Presence.unlink from within the test but was unable to get any other results.

I’m seeing the following error:

09:32:22.414 [error] Task #PID<0.580.0> started from MyApp.Presence terminating
** (stop) exited in: GenServer.call(#PID<0.577.0>, {:checkout, #Reference<0.0.5.2491>, true, 15000}, 5000)
    ** (EXIT) shutdown: "owner #PID<0.576.0> exited while client #PID<0.579.0> is still running with: shutdown"
    (db_connection) lib/db_connection/ownership/proxy.ex:32: DBConnection.Ownership.Proxy.checkout/2
    (db_connection) lib/db_connection.ex:919: DBConnection.checkout/2
    (db_connection) lib/db_connection.ex:741: DBConnection.run/3
    (db_connection) lib/db_connection.ex:584: DBConnection.prepare_execute/4
    (ecto) lib/ecto/adapters/postgres/connection.ex:80: Ecto.Adapters.Postgres.Connection.prepare_execute/5
    (ecto) lib/ecto/adapters/sql.ex:243: Ecto.Adapters.SQL.sql_call/6
    (ecto) lib/ecto/adapters/sql.ex:431: Ecto.Adapters.SQL.execute_and_cache/7
    (ecto) lib/ecto/repo/queryable.ex:130: Ecto.Repo.Queryable.execute/5
    (ecto) lib/ecto/repo/queryable.ex:35: Ecto.Repo.Queryable.all/4
    (my_app) lib/my_app/presence.ex:17: MyApp.Presence.fetch/2
    (phoenix) lib/phoenix/presence.ex:199: anonymous fn/5 in Phoenix.Presence.handle_diff/5
    (stdlib) lists.erl:1263: :lists.foldl/3
    (phoenix) lib/phoenix/presence.ex:197: anonymous fn/4 in Phoenix.Presence.handle_diff/5
    (elixir) lib/task/supervised.ex:85: Task.Supervised.do_apply/2
    (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
Function: #Function<1.96140178/0 in Phoenix.Presence.handle_diff/5>
    Args: []

Using this channel module:

defmodule MyApp.ExampleChannel do
  use MyApp.Web, :channel

  def join(_channel_name, _params, socket) do
    send self(), :after_join

    {:ok, socket}
  end

  def handle_info(:after_join, socket) do
    current_user = socket.assigns.current_user

    {:ok, _} = Presence.track(socket, current_user.id, %{})

    {:noreply, socket}
  end
end

this presence module:

defmodule MyApp.Presence do
  import Ecto.Query
  alias MyApp.User
  alias MyApp.Repo

  use Phoenix.Presence, otp_app: :MyApp,
                        pubsub_server: MyApp.PubSub

  def fetch(_topic, entries) do
    query =
      from u in User,
        where: u.id in ^Map.keys(entries),
        select: {u.id, u}

    users = query |> Repo.all |> Enum.into(%{})

    for { key, %{ metas: metas } } <- entries, into: %{} do
      int_key = String.to_integer(key)
      { key, %{ metas: metas, user: users[int_key] } }
    end
  end
end

and this channel test:

defmodule MyApp.ExampleChannelTest do
  use MyApp.ChannelCase

  alias MyApp.ExampleChannel

  test 'example' do
    user = create_a_user

    params = %{ current_user: user }
    {:ok, _, socket} = subscribe_and_join(socket("", params), ExampleChannel, "control")
  end
end

Any help is greatly appreciated. Thanks!

2 Likes

Hi there :slight_smile: Did you find a solution to this? Has anyone also had this problem?

(Sorry to bring back an old post, but it describes exactly the same issue I’m having.)

As a temporary solution, adding this code at the end of the channel test

ref = leave(socket)
assert_reply ref, :ok
IO.puts "socket leave"
:timer.sleep(200)

makes the fetch function in Presence be called before the test finishes, which works with the Ecto’s sandbox shared strategy. If I remove the :timer.sleep call, the error continues.

** (stop) exited in: GenServer.call(#PID<0.384.0>, {:checkout, 
   #Reference<0.1150698256.1547436035.131411>, true, 15000}, 5000)
** (EXIT) shutdown: "owner #PID<0.383.0> exited with: shutdown"

I never actually found a solution for this, but with our app we ended up removing the fetch function entirely. Now we just return user IDs and match them up with user data sent via other channels.

1 Like

This is the correct solution in my experience. You must leave before the test is complete while the sandbox connection is still checked out—it also has to be synchronous to enable automatic sharing, as there isn’t any way to allow the presence process access to the test’s db connection.

The sleep doesn’t have to be nearly so long as 200ms though. The helper function I have uses a 10ms delay and doesn’t flicker on low powered systems like CI.

1 Like

That’s great to hear, thanks. Just for fun, sleeping for 4ms ~ 5ms works about 50% of the time on my machine.

I’ll try to submit a pull request for the Phoenix Presence docs with the info from this thread :slight_smile:

1 Like