refactor(web): add test-utils helpers for likes/quarantine/track/appState mocks (#375)

Pre-sweep checkpoint. Adds:
- fixtures/track.ts        — makeTrack() / makeTracks(n) (18 files duplicate today)
- mocks/likes.ts           — emptyLikesMock() (19 files duplicate today)
- mocks/quarantine.ts      — emptyQuarantineMock() (9 files duplicate today)
- mocks/appState.ts        — pageUrlModule(state) (8 files duplicate today)

The sweep commits that follow update test files to use these helpers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/test-utils/fixtures/track.ts

@@ -0,0 +1,31 @@
+// Fixture builders for TrackRef. Use in test setup to avoid
+// re-declaring the same literal across 18+ files.
+
+import type { TrackRef } from '$lib/api/types';
+
+export function makeTrack(overrides: Partial<TrackRef> = {}): TrackRef {
+  return {
+    id: 't1',
+    title: 'Test Track',
+    album_id: 'a1',
+    album_title: 'Test Album',
+    artist_id: 'ar1',
+    artist_name: 'Test Artist',
+    track_number: 1,
+    disc_number: 1,
+    duration_sec: 180,
+    stream_url: '/api/tracks/t1/stream',
+    ...overrides
+  };
+}
+
+export function makeTracks(n: number, overrides: Partial<TrackRef> = {}): TrackRef[] {
+  return Array.from({ length: n }, (_, i) =>
+    makeTrack({
+      id: `t${i + 1}`,
+      title: `Test Track ${i + 1}`,
+      stream_url: `/api/tracks/t${i + 1}/stream`,
+      ...overrides
+    })
+  );
+}

web/src/test-utils/mocks/appState.ts

@@ -0,0 +1,22 @@
+// $app/state mock factory. The vi.hoisted state holder still has to
+// live in each test file (vitest mock-hoisting transform requires
+// it) but the getter shape is centralized here.
+//
+// Usage:
+//   const pageState = vi.hoisted(() => ({
+//     pageUrl: new URL('http://localhost/search?q=miles')
+//   }));
+//   vi.mock('$app/state', () => pageUrlModule(pageState));
+//   afterEach(() => { pageState.pageUrl = new URL('http://localhost/search?q=miles'); });
+
+export type PageUrlState = { pageUrl: URL };
+
+export function pageUrlModule(state: PageUrlState) {
+  return {
+    page: {
+      get url() {
+        return state.pageUrl;
+      }
+    }
+  };
+}

web/src/test-utils/mocks/likes.ts

@@ -0,0 +1,25 @@
+// Default empty-LikedIds mock for $lib/api/likes. Mirrors the
+// TanStack Query readable shape (data + isPending + isError) that
+// 19 test files were duplicating verbatim.
+//
+// Usage:
+//   vi.mock('$lib/api/likes', () => emptyLikesMock());
+//
+// Tests that assert on liked-state changes (LikeButton.test.ts) keep
+// their state-driven mocks inline.
+
+import { readable } from 'svelte/store';
+import { vi } from 'vitest';
+
+export function emptyLikesMock() {
+  return {
+    createLikedIdsQuery: () =>
+      readable({
+        data: { track_ids: [], album_ids: [], artist_ids: [] },
+        isPending: false,
+        isError: false
+      }),
+    likeEntity: vi.fn().mockResolvedValue(undefined),
+    unlikeEntity: vi.fn().mockResolvedValue(undefined)
+  };
+}

web/src/test-utils/mocks/quarantine.ts

@@ -0,0 +1,21 @@
+// Default empty-quarantine mock for $lib/api/quarantine. The
+// dominant shape across 9 test files: empty list + spy mutations.
+//
+// Usage:
+//   vi.mock('$lib/api/quarantine', () => emptyQuarantineMock());
+//
+// Tests that assert on per-row state (FlagPopover, playlist tests)
+// keep custom mocks inline.
+
+import { readable } from 'svelte/store';
+import { vi } from 'vitest';
+
+export function emptyQuarantineMock() {
+  return {
+    flagTrack: vi.fn().mockResolvedValue({}),
+    unflagTrack: vi.fn().mockResolvedValue(undefined),
+    listMyQuarantine: vi.fn().mockResolvedValue([]),
+    createMyQuarantineQuery: () =>
+      readable({ data: [], isPending: false, isError: false })
+  };
+}