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!