diff --git a/frontend/src/components/PlexCollectionView.dom.test.tsx b/frontend/src/components/PlexCollectionView.dom.test.tsx
new file mode 100644
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+++ b/frontend/src/components/PlexCollectionView.dom.test.tsx
@@ -0,0 +1,128 @@
+// @vitest-environment jsdom
+//
+// S4 Play-all — buildQueue's show→episode expansion and playAll's decision branch, the honest-states
+// behaviour the deep-review flagged as untested. A leaf member queues as itself; a show member is
+// expanded (lazily, on click) into its episodes in season→episode order; a show that expands to zero
+// episodes must NOT silently no-op but surface the `playEmpty` info notice. api.plexCollection /
+// api.plexShow are stubbed so the queries resolve synchronously; notify is spied to assert the notice.
+import { describe, it, expect, vi, beforeAll, afterEach } from "vitest";
+import { render, screen, fireEvent, waitFor, cleanup } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+beforeAll(() => {
+  // Poster grids / carousels wire a ResizeObserver; jsdom ships none.
+  class Stub {
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+    takeRecords() {
+      return [];
+    }
+  }
+  globalThis.ResizeObserver ??= Stub as unknown as typeof ResizeObserver;
+});
+
+vi.mock("react-i18next", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("react-i18next")>();
+  return { ...actual, useTranslation: () => ({ t: (key: string) => key }) };
+});
+vi.mock("./ConfirmProvider", () => ({ useConfirm: () => async () => true }));
+
+// Spy notify without dropping the module's other exports (the render subtree uses them).
+const h = vi.hoisted(() => ({ notify: vi.fn() }));
+vi.mock("../lib/notifications", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("../lib/notifications")>()),
+  notify: (...a: unknown[]) => h.notify(...a),
+}));
+
+import PlexCollectionView from "./PlexCollectionView";
+import { api, type PlexCard, type PlexCollectionDetail, type PlexShowDetail } from "../lib/api";
+
+afterEach(() => {
+  cleanup();
+  vi.restoreAllMocks();
+  h.notify.mockClear();
+});
+
+const card = (id: string, type: "movie" | "show"): PlexCard =>
+  ({
+    id,
+    type,
+    title: id,
+    year: 2000,
+    duration_seconds: 3600,
+    thumb: `/api/plex/image/${id}`,
+    playable: "direct",
+    status: "new",
+    position_seconds: 0,
+  }) as unknown as PlexCard;
+
+const detail = (items: PlexCard[]): PlexCollectionDetail =>
+  ({
+    id: "col1",
+    title: "My Collection",
+    thumb: "/api/plex/image/col1",
+    year_min: null,
+    year_max: null,
+    content_rating: null,
+    child_count: items.length,
+    total_runtime_s: 0,
+    items,
+    can_edit: false,
+    editable: false,
+  }) as unknown as PlexCollectionDetail;
+
+const showDetail = (episodeIds: string[][]): PlexShowDetail =>
+  ({
+    seasons: episodeIds.map((eps) => ({ episodes: eps.map((id) => ({ id })) })),
+  }) as unknown as PlexShowDetail;
+
+function mount(items: PlexCard[], onPlay = vi.fn()) {
+  vi.spyOn(api, "plexCollection").mockResolvedValue(detail(items));
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  render(
+    <QueryClientProvider client={qc}>
+      <PlexCollectionView
+        collectionId="col1"
+        onBack={() => {}}
+        onPlay={onPlay}
+        onOpenCard={() => {}}
+        onInfoCard={() => {}}
+      />
+    </QueryClientProvider>,
+  );
+  return onPlay;
+}
+
+describe("PlexCollectionView — Play-all", () => {
+  it("queues a leaf member as itself", async () => {
+    const onPlay = mount([card("movie1", "movie")]);
+    fireEvent.click(await screen.findByText("plex.collection.playAll"));
+    await waitFor(() => expect(onPlay).toHaveBeenCalledTimes(1));
+    expect(onPlay).toHaveBeenCalledWith("movie1", ["movie1"]);
+    expect(h.notify).not.toHaveBeenCalled();
+  });
+
+  it("expands a show member into its episodes in season→episode order", async () => {
+    const spyShow = vi
+      .spyOn(api, "plexShow")
+      .mockResolvedValue(showDetail([["s1e1", "s1e2"], ["s2e1"]]));
+    const onPlay = mount([card("show1", "show")]);
+    fireEvent.click(await screen.findByText("plex.collection.playAll"));
+    await waitFor(() => expect(onPlay).toHaveBeenCalledTimes(1));
+    expect(spyShow).toHaveBeenCalledWith("show1");
+    expect(onPlay).toHaveBeenCalledWith("s1e1", ["s1e1", "s1e2", "s2e1"]);
+  });
+
+  it("surfaces the playEmpty notice (not a silent no-op) when a show expands to zero episodes", async () => {
+    vi.spyOn(api, "plexShow").mockResolvedValue(showDetail([])); // no seasons → empty queue
+    const onPlay = mount([card("show1", "show")]);
+    fireEvent.click(await screen.findByText("plex.collection.playAll"));
+    await waitFor(() =>
+      expect(h.notify).toHaveBeenCalledWith(
+        expect.objectContaining({ level: "info", message: "plex.collection.playEmpty" }),
+      ),
+    );
+    expect(onPlay).not.toHaveBeenCalled();
+  });
+});