chore: migrate tests from tests-ui/ to colocate with source files (#7811)

## Summary

Migrates all unit tests from `tests-ui/` to colocate with their source
files in `src/`, improving discoverability and maintainability.

## Changes

- **What**: Relocated all unit tests to be adjacent to the code they
test, following the `<source>.test.ts` naming convention
- **Config**: Updated `vitest.config.ts` to remove `tests-ui` include
pattern and `@tests-ui` alias
- **Docs**: Moved testing documentation to `docs/testing/` with updated
paths and patterns

## Review Focus

- Migration patterns documented in
`temp/plans/migrate-tests-ui-to-src.md`
- Tests use `@/` path aliases instead of relative imports
- Shared fixtures placed in `__fixtures__/` directories

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7811-chore-migrate-tests-from-tests-ui-to-colocate-with-source-files-2da6d73d36508147a4cce85365dee614)
by [Unito](https://www.unito.io)

---------

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

src/renderer/extensions/vueNodes/widgets/components/WidgetSelect.asset-mode.test.ts

@@ -0,0 +1,89 @@
+import { createTestingPinia } from '@pinia/testing'
+import { flushPromises, mount } from '@vue/test-utils'
+import PrimeVue from 'primevue/config'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import type { SimplifiedWidget } from '@/types/simplifiedWidget'
+
+import WidgetSelect from '@/renderer/extensions/vueNodes/widgets/components/WidgetSelect.vue'
+
+// Mock modules
+vi.mock('@/platform/distribution/types', () => ({
+  isCloud: true
+}))
+
+vi.mock('@/platform/assets/services/assetService', () => ({
+  assetService: {
+    isAssetBrowserEligible: vi.fn(() => true)
+  }
+}))
+
+const mockSettingStoreGet = vi.fn()
+
+vi.mock('@/platform/settings/settingStore', () => ({
+  useSettingStore: vi.fn(() => ({
+    get: mockSettingStoreGet
+  }))
+}))
+
+// Import after mocks are defined
+import { assetService } from '@/platform/assets/services/assetService'
+const mockAssetServiceEligible = vi.mocked(assetService.isAssetBrowserEligible)
+
+describe('WidgetSelect asset mode', () => {
+  const createWidget = (): SimplifiedWidget<string | undefined> => ({
+    name: 'ckpt_name',
+    type: 'combo',
+    value: undefined,
+    options: {
+      values: []
+    }
+  })
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+    mockAssetServiceEligible.mockReturnValue(true)
+    mockSettingStoreGet.mockReturnValue(true) // Default to true for UseAssetAPI
+  })
+
+  // Helper to mount with common setup
+  const mountWidget = () => {
+    return mount(WidgetSelect, {
+      props: {
+        widget: createWidget(),
+        modelValue: undefined,
+        nodeType: 'CheckpointLoaderSimple'
+      },
+      global: {
+        plugins: [PrimeVue, createTestingPinia()]
+      }
+    })
+  }
+
+  it('uses dropdown when isCloud && UseAssetAPI && isEligible', async () => {
+    const wrapper = mountWidget()
+    await flushPromises()
+
+    expect(
+      wrapper.findComponent({ name: 'WidgetSelectDropdown' }).exists()
+    ).toBe(true)
+  })
+
+  it('uses default widget when UseAssetAPI setting is false', () => {
+    mockSettingStoreGet.mockReturnValue(false)
+    const wrapper = mountWidget()
+
+    expect(
+      wrapper.findComponent({ name: 'WidgetSelectDefault' }).exists()
+    ).toBe(true)
+  })
+
+  it('uses default widget when node is not eligible', () => {
+    mockAssetServiceEligible.mockReturnValue(false)
+    const wrapper = mountWidget()
+
+    expect(
+      wrapper.findComponent({ name: 'WidgetSelectDefault' }).exists()
+    ).toBe(true)
+  })
+})