Fix issue with new elements in stream DOM test (#2677)

This resolves an issue for testing streams. New items didn't get assigned the data-phx-stream and thus subsequent stream resets didn't reset the list as the previously added items couldn't be matched for the data-phx-stream.

Co-authored-by: Chris McCord <[email protected]>

lib/phoenix_live_view/test/dom.ex

@@ -445,9 +445,11 @@ defmodule Phoenix.LiveViewTest.DOM do
                 child -> set_attr(child, "data-phx-stream", ref)
               end
 
+            parent_id = parent_id(html_tree, id)
+
             cond do
               # skip added children that aren't ours if they are not being appended
-              not_appended? and parent_id(html_tree, id) != container_id ->
+              not_appended? && parent_id && parent_id != container_id ->
                 acc
 
               # do not append existing child if already present, only update in place

test/phoenix_live_view/integrations/stream_test.exs

@@ -139,6 +139,20 @@ defmodule Phoenix.LiveView.StreamTest do
 
     refute has_element?(lv, "li", "Apples")
     refute has_element?(lv, "li", "Oranges")
+
+    lv
+    |> element("a", "Switch")
+    |> render_click()
+
+    assert_patched(lv, "/healthy/fruits")
+
+    assert has_element?(lv, "h1", "Fruits")
+
+    refute has_element?(lv, "li", "Carrots")
+    refute has_element?(lv, "li", "Tomatoes")
+
+    assert has_element?(lv, "li", "Apples")
+    assert has_element?(lv, "li", "Oranges")
   end
 
   describe "within live component" do