Testing LiveView and Presence: How to simulate a user has left (e.g. closed tab)

You could always just kill the process:

{:ok, lv, _html} = live(conn, ~p"/the-page")

Process.exit(lv.pid, :kill)

If there is a cleaner way I am not sure.

I tried that, it causes the whole test to fail:

21:35:39.842 [error] GenServer #PID<0.465.0> terminating
** (stop) killed
Last message: {:EXIT, #PID<0.461.0>, :killed}

  1) test PageLive renders expected presence data (ProjectWeb.StatsLiveTest)
     test/project_web/live/stats_live_test.exs:76
     ** (EXIT from #PID<0.461.0>) killed

Dang, I’m also interested, though. I’ve only ever tested this stuff with Wallaby.

Can you post your whole test?

It’s a really long test, so there’s a lot of cruft. I tried making a barebones version and it’s not crashing the whole test anymore. I’ll poke around for a bit and see if I can find out what is causing the issue.

Thanks for the hint. I have to make dinner so I’ll be back with more info in a bit.

It looks like killing the LiveView process causes the test to crash pretty much immediately. This example will crash:

  test "test crash example", %{conn: conn, quiz: quiz} do
    {:ok, view, html} = conn |> live(~p"/contact-us")
    Process.exit(view.pid(), :kill)
    Process.sleep(1)
  end

I’m in over my head on this one. Until I can figure out how to gracefully end the LiveView processes, I’m just gonna stick to my simulated link-clicking hack.

Try Process.exit(view.pid, :normal). Docs: Process — Elixir v1.15.5

Using :normal does not appear to have any effect.

Here’s a brief version of the test I’ve been working with (it’s for a toy project where multiple users can take a quiz while a teacher supervises the results):

    test "renders expected presence data as the user progresses through the quiz", %{
      conn: conn,
      quiz: quiz
    } do
      {:ok, quiz_stats_view, html} = conn |> live(_get_quiz_stats_url(quiz.id))

      # quiz_stats: template contains expected content before user joins the quiz lobby
      assert html =~ "No users are preparing to take this quiz."

      ## quiz_take: unauthenticated user joins the quiz lobby
      {:ok, quiz_take_view, _html} = build_conn() |> live(_get_quiz_take_url(quiz.id))

      # quiz_stats: template no longer contains initial content after receiving Presence data broadcast
      Process.sleep(5)
      user_joined_html = render(quiz_stats_view)

      refute user_joined_html =~ "No users are preparing to take this quiz."

      # quiz_stats: template contains placeholder text for unauthenticated user with no name
      assert html_element_has_content(
               user_joined_html,
               ~s|[data-test-id="users-not-yet-started"]|,
               "No name yet"
             )

      ## quiz_take: user leaves the page (hacky, but it works)
      # quiz_take_view |> element(~s|a|, "Exit this quiz") |> render_click()

      ## quiz_take: user leaves the page (not hacky, but crashes the test)
      Process.exit(quiz_take_view.pid(), :normal)

      # quiz_stats: template no longer contains information about this user
      Process.sleep(5)
      user_exited_html = render(quiz_stats_view)
      refute user_exited_html =~ "No name yet"
    end

To recap: Process.exit(quiz_take_view.pid(), :kill) crashes the entire test, and Process.exit(quiz_take_view.pid(), :normal) appears to have no effect whatsoever (even after a lengthy Process.sleep(30_000)). Simulating a link being clicked seems to shut down the view gracefully (thus the test can complete successfully), but I have no idea what’s going on behind the scenes (I’ve looked, but there’s a lot going on that goes above my head).

Tested on Elixir 1.15.5-otp-26 on Linux.

The issue is that two things are started. A LV client and a channel for communication. Both seem to be linked to the test process. Most of that stuff is private though. stop_supervised(view.pid) seems to work, though with a warning. I’d argue that LV should provide an API to close a view.

Finally got it! GenServer.stop(view.pid()) did the trick.

To simulate a user being unauthenticated and disconnected in all liveviews and channels you can do:

MyAppWeb.Endpoint.broadcast("users_socket:#{user.id}", "disconnect", %{})

This covered in the documentation here Disconnecting all instances of a live user.