test(infra): AssetHelper with builder pattern + deterministic fixtures (#10545)

## What

Adds `AssetHelper` — a builder-pattern helper for mocking asset-related
API endpoints in Playwright E2E tests, plus deterministic fixture data.

## Why

12+ asset-related API endpoints need mocking for asset browser tests
(PNL-02), cloud dialog testing (DLG-08), and other asset-dependent E2E
scenarios. Random mock data from existing `createMockAssets()` is
unsuitable for deterministic E2E assertions.

## What's included

### `AssetHelper.ts` (307 LOC)
- Fluent builder API: `assetHelper.withModels(3).withImages(5).mock()`
- Stateful mock store (Map) for upload→verify→delete flows
- Endpoint coverage: GET/POST/PUT/DELETE `/assets`, download progress
- `mockError()` for error state testing
- `clearMocks()` cleanup matching QueueHelper/FeatureFlagHelper pattern

### `assetFixtures.ts` (304 LOC)
- 11 stable named constants (checkpoints, loras, VAE, embedding, inputs,
outputs)
- Factory functions: `generateModels()`, `generateInputFiles()`,
`generateOutputAssets()`
- Fixed IDs/dates/sizes — no randomness, safe for screenshot comparisons

### ComfyPage integration
- Available as `comfyPage.assets` in all tests

## Testing
- TypeScript compiles clean
- Follows existing QueueHelper/FeatureFlagHelper conventions

## Unblocks
- PNL-02: Asset browser tests (@Jaewon Yoon)
- DLG-08: Assets modal / cloud dialog testing

Part of: Test Coverage Q2 Overhaul

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10545-test-infra-AssetHelper-with-builder-pattern-deterministic-fixtures-32f6d73d365081d3985ef079ff3dbede)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

browser_tests/tests/assetHelper.spec.ts

@@ -0,0 +1,382 @@
+import { expect } from '@playwright/test'
+
+import { comfyPageFixture as test } from '../fixtures/ComfyPage'
+import {
+  createAssetHelper,
+  withModels,
+  withInputFiles,
+  withOutputAssets,
+  withAsset,
+  withPagination,
+  withUploadResponse
+} from '../fixtures/helpers/AssetHelper'
+import {
+  STABLE_CHECKPOINT,
+  STABLE_LORA,
+  STABLE_INPUT_IMAGE,
+  STABLE_OUTPUT
+} from '../fixtures/data/assetFixtures'
+
+test.describe('AssetHelper', () => {
+  test.describe('operators and configuration', () => {
+    test('creates helper with models via withModels operator', async ({
+      comfyPage
+    }) => {
+      const helper = createAssetHelper(
+        comfyPage.page,
+        withModels(3, 'checkpoints')
+      )
+      expect(helper.assetCount).toBe(3)
+      expect(
+        helper.getAssets().every((a) => a.tags?.includes('checkpoints'))
+      ).toBe(true)
+    })
+
+    test('composes multiple operators', async ({ comfyPage }) => {
+      const helper = createAssetHelper(
+        comfyPage.page,
+        withModels(2, 'checkpoints'),
+        withInputFiles(2),
+        withOutputAssets(1)
+      )
+      expect(helper.assetCount).toBe(5)
+    })
+
+    test('adds individual assets via withAsset', async ({ comfyPage }) => {
+      const helper = createAssetHelper(
+        comfyPage.page,
+        withAsset(STABLE_CHECKPOINT),
+        withAsset(STABLE_LORA)
+      )
+      expect(helper.assetCount).toBe(2)
+      expect(helper.getAsset(STABLE_CHECKPOINT.id)).toMatchObject({
+        id: STABLE_CHECKPOINT.id,
+        name: STABLE_CHECKPOINT.name
+      })
+    })
+
+    test('withPagination sets pagination options', async ({ comfyPage }) => {
+      const helper = createAssetHelper(
+        comfyPage.page,
+        withModels(2),
+        withPagination({ total: 100, hasMore: true })
+      )
+      expect(helper.assetCount).toBe(2)
+    })
+  })
+
+  test.describe('mock API routes', () => {
+    test('GET /assets returns all assets', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(
+        withAsset(STABLE_CHECKPOINT),
+        withAsset(STABLE_INPUT_IMAGE)
+      )
+      await assetApi.mock()
+
+      const { status, body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets`
+      )
+      expect(status).toBe(200)
+
+      const data = body as {
+        assets: unknown[]
+        total: number
+        has_more: boolean
+      }
+      expect(data.assets).toHaveLength(2)
+      expect(data.total).toBe(2)
+      expect(data.has_more).toBe(false)
+
+      await assetApi.clearMocks()
+    })
+
+    test('GET /assets respects pagination params', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(
+        withModels(5),
+        withPagination({ total: 10, hasMore: true })
+      )
+      await assetApi.mock()
+
+      const { body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets?limit=2&offset=0`
+      )
+      const data = body as {
+        assets: unknown[]
+        total: number
+        has_more: boolean
+      }
+      expect(data.assets).toHaveLength(2)
+      expect(data.total).toBe(10)
+      expect(data.has_more).toBe(true)
+
+      await assetApi.clearMocks()
+    })
+
+    test('GET /assets filters by include_tags', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(
+        withAsset(STABLE_CHECKPOINT),
+        withAsset(STABLE_LORA),
+        withAsset(STABLE_INPUT_IMAGE)
+      )
+      await assetApi.mock()
+
+      const { body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets?include_tags=models,checkpoints`
+      )
+      const data = body as { assets: Array<{ id: string }> }
+      expect(data.assets).toHaveLength(1)
+      expect(data.assets[0].id).toBe(STABLE_CHECKPOINT.id)
+
+      await assetApi.clearMocks()
+    })
+
+    test('GET /assets/:id returns single asset or 404', async ({
+      comfyPage
+    }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(withAsset(STABLE_CHECKPOINT))
+      await assetApi.mock()
+
+      const found = await assetApi.fetch(
+        `${comfyPage.url}/api/assets/${STABLE_CHECKPOINT.id}`
+      )
+      expect(found.status).toBe(200)
+      const asset = found.body as { id: string }
+      expect(asset.id).toBe(STABLE_CHECKPOINT.id)
+
+      const notFound = await assetApi.fetch(
+        `${comfyPage.url}/api/assets/nonexistent-id`
+      )
+      expect(notFound.status).toBe(404)
+
+      await assetApi.clearMocks()
+    })
+
+    test('PUT /assets/:id updates asset in store', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(withAsset(STABLE_CHECKPOINT))
+      await assetApi.mock()
+
+      const { status, body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets/${STABLE_CHECKPOINT.id}`,
+        {
+          method: 'PUT',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify({ name: 'renamed.safetensors' })
+        }
+      )
+      expect(status).toBe(200)
+
+      const updated = body as { name: string }
+      expect(updated.name).toBe('renamed.safetensors')
+      expect(assetApi.getAsset(STABLE_CHECKPOINT.id)?.name).toBe(
+        'renamed.safetensors'
+      )
+
+      await assetApi.clearMocks()
+    })
+
+    test('DELETE /assets/:id removes asset from store', async ({
+      comfyPage
+    }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(withAsset(STABLE_CHECKPOINT), withAsset(STABLE_LORA))
+      await assetApi.mock()
+
+      const { status } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets/${STABLE_CHECKPOINT.id}`,
+        { method: 'DELETE' }
+      )
+      expect(status).toBe(204)
+      expect(assetApi.assetCount).toBe(1)
+      expect(assetApi.getAsset(STABLE_CHECKPOINT.id)).toBeUndefined()
+
+      await assetApi.clearMocks()
+    })
+
+    test('POST /assets returns upload response', async ({ comfyPage }) => {
+      const customUpload = {
+        id: 'custom-upload-001',
+        name: 'custom.safetensors',
+        tags: ['models'],
+        created_at: '2025-01-01T00:00:00Z',
+        created_new: true
+      }
+      const { assetApi } = comfyPage
+      assetApi.configure(withUploadResponse(customUpload))
+      await assetApi.mock()
+
+      const { status, body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets`,
+        { method: 'POST' }
+      )
+      expect(status).toBe(201)
+      const data = body as { id: string; name: string }
+      expect(data.id).toBe('custom-upload-001')
+      expect(data.name).toBe('custom.safetensors')
+
+      await assetApi.clearMocks()
+    })
+
+    test('POST /assets/download returns async download response', async ({
+      comfyPage
+    }) => {
+      const { assetApi } = comfyPage
+      await assetApi.mock()
+
+      const { status, body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets/download`,
+        { method: 'POST' }
+      )
+      expect(status).toBe(202)
+      const data = body as { task_id: string; status: string }
+      expect(data.task_id).toBe('download-task-001')
+      expect(data.status).toBe('created')
+
+      await assetApi.clearMocks()
+    })
+  })
+
+  test.describe('mutation tracking', () => {
+    test('tracks POST, PUT, DELETE mutations', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(withAsset(STABLE_CHECKPOINT))
+      await assetApi.mock()
+
+      await assetApi.fetch(`${comfyPage.url}/api/assets`, { method: 'POST' })
+      await assetApi.fetch(
+        `${comfyPage.url}/api/assets/${STABLE_CHECKPOINT.id}`,
+        {
+          method: 'PUT',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify({ name: 'updated.safetensors' })
+        }
+      )
+      await assetApi.fetch(
+        `${comfyPage.url}/api/assets/${STABLE_CHECKPOINT.id}`,
+        { method: 'DELETE' }
+      )
+
+      const mutations = assetApi.getMutations()
+      expect(mutations).toHaveLength(3)
+      expect(mutations[0].method).toBe('POST')
+      expect(mutations[1].method).toBe('PUT')
+      expect(mutations[2].method).toBe('DELETE')
+
+      await assetApi.clearMocks()
+    })
+
+    test('GET requests are not tracked as mutations', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(withAsset(STABLE_CHECKPOINT))
+      await assetApi.mock()
+
+      await assetApi.fetch(`${comfyPage.url}/api/assets`)
+      await assetApi.fetch(
+        `${comfyPage.url}/api/assets/${STABLE_CHECKPOINT.id}`
+      )
+
+      expect(assetApi.getMutations()).toHaveLength(0)
+
+      await assetApi.clearMocks()
+    })
+  })
+
+  test.describe('mockError', () => {
+    test('returns error status for all asset routes', async ({ comfyPage }) => {
+      const { assetApi } = comfyPage
+      await assetApi.mockError(503, 'Service Unavailable')
+
+      const { status, body } = await assetApi.fetch(
+        `${comfyPage.url}/api/assets`
+      )
+      expect(status).toBe(503)
+      const data = body as { error: string }
+      expect(data.error).toBe('Service Unavailable')
+
+      await assetApi.clearMocks()
+    })
+  })
+
+  test.describe('clearMocks', () => {
+    test('resets store, mutations, and unroutes handlers', async ({
+      comfyPage
+    }) => {
+      const { assetApi } = comfyPage
+      assetApi.configure(withAsset(STABLE_CHECKPOINT))
+      await assetApi.mock()
+
+      await assetApi.fetch(`${comfyPage.url}/api/assets`, { method: 'POST' })
+      expect(assetApi.getMutations()).toHaveLength(1)
+      expect(assetApi.assetCount).toBe(1)
+
+      await assetApi.clearMocks()
+      expect(assetApi.getMutations()).toHaveLength(0)
+      expect(assetApi.assetCount).toBe(0)
+    })
+  })
+
+  test.describe('fixture generators', () => {
+    test('generateModels produces deterministic assets', async ({
+      comfyPage
+    }) => {
+      const helper = createAssetHelper(comfyPage.page, withModels(3, 'loras'))
+      const assets = helper.getAssets()
+
+      expect(assets).toHaveLength(3)
+      expect(assets.every((a) => a.tags?.includes('loras'))).toBe(true)
+      expect(assets.every((a) => a.tags?.includes('models'))).toBe(true)
+
+      const ids = assets.map((a) => a.id)
+      expect(new Set(ids).size).toBe(3)
+    })
+
+    test('generateInputFiles produces deterministic input assets', async ({
+      comfyPage
+    }) => {
+      const helper = createAssetHelper(comfyPage.page, withInputFiles(3))
+      const assets = helper.getAssets()
+
+      expect(assets).toHaveLength(3)
+      expect(assets.every((a) => a.tags?.includes('input'))).toBe(true)
+    })
+
+    test('generateOutputAssets produces deterministic output assets', async ({
+      comfyPage
+    }) => {
+      const helper = createAssetHelper(comfyPage.page, withOutputAssets(5))
+      const assets = helper.getAssets()
+
+      expect(assets).toHaveLength(5)
+      expect(assets.every((a) => a.tags?.includes('output'))).toBe(true)
+      expect(assets.every((a) => a.name.startsWith('ComfyUI_'))).toBe(true)
+    })
+
+    test('stable fixtures have expected properties', async ({ comfyPage }) => {
+      const helper = createAssetHelper(
+        comfyPage.page,
+        withAsset(STABLE_CHECKPOINT),
+        withAsset(STABLE_LORA),
+        withAsset(STABLE_INPUT_IMAGE),
+        withAsset(STABLE_OUTPUT)
+      )
+
+      const checkpoint = helper.getAsset(STABLE_CHECKPOINT.id)!
+      expect(checkpoint.tags).toContain('checkpoints')
+      expect(checkpoint.size).toBeGreaterThan(0)
+      expect(checkpoint.created_at).toBeTruthy()
+
+      const lora = helper.getAsset(STABLE_LORA.id)!
+      expect(lora.tags).toContain('loras')
+
+      const input = helper.getAsset(STABLE_INPUT_IMAGE.id)!
+      expect(input.tags).toContain('input')
+
+      const output = helper.getAsset(STABLE_OUTPUT.id)!
+      expect(output.tags).toContain('output')
+    })
+  })
+})