Stream reset behaviour changed in 1.1.9 in LiveViewTest

[Aratramba]

Environment

• Elixir version (elixir -v): Elixir 1.18.1 (compiled with Erlang/OTP 27)
• Phoenix version (mix deps): 1.8
• Phoenix LiveView version (mix deps): 1.1.12
• Operating system: OSX
• Browsers you attempted to reproduce this bug on (the more the merrier): -
• Does the problem persist after removing "assets/node_modules" and trying again? Yes/no: Yes

Actual behavior

Release 1.1.9 introduced a change that broke one of my tests relating to streams. I can't quite figure out what it was exactly by looking through the changelogs. It seems only related to tests.

See this standalone test liveview-1.1.9-stream-reset.exs.txt. Changing the phoenix_live_view dependency from 1.1.9 to 1.1.8 will make it pass.

I'm rendering a stream:

  @impl Phoenix.LiveView
  def render(assigns) do
    ~H"""
    <ul id="items" phx-update="stream">
      <li :for={{dom_id, item} <- @streams.items} id={dom_id}>
        {item.name}
      </li>
    </ul>
    """
  end

On mount I create the stream

  def mount(_params, _session, socket) do
    {:ok,
     socket
     |> stream_configure(:items, dom_id: &"item-#{&1.uuid}")
     |> stream(:items, [])}
  end

In handle params I reset it

  def handle_params(_params, _uri, socket) do
    paginated_items = paginate_items(0, 3)

    {:noreply,
     socket
     |> assign(:page, 0)
     |> stream(:items, paginated_items, reset: true)}
  end

In the test i simulate a hook call to load more

  def handle_event("load-more", %{}, socket) do
    new_page = socket.assigns.page + 1

    paginated_items = paginate_items(new_page * 3, 3)

    {:noreply,
     socket
     |> stream(:items, paginated_items, at: -1)
     |> assign(:page, new_page)}
  end

html = render_hook(view, "load-more", %{})

This used to add 3 items to the list.
Since 1.1.9 it replaces the existing items with 3 new ones.

Expected behaviour

The test passes in LiveView 1.1.8, but breaks in 1.1.9.

In LiveView 1.1.8 this resulted in 6 items after the render hook call.
In LiveView 1.1.9 this results in 3 new items after the render hook call.

If I change to reset: false in handle_params, it passes in 1.1.9.

[SteffenDE]

Thank you, will be fixed with #3994!