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/scripts/api.fetchApi.test.ts

@@ -0,0 +1,171 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { api } from '@/scripts/api'
+
+// Mock global fetch
+vi.stubGlobal('fetch', vi.fn())
+
+describe('api.fetchApi', () => {
+  beforeEach(() => {
+    vi.resetAllMocks()
+
+    // Reset api state
+    api.user = 'test-user'
+  })
+
+  describe('header handling', () => {
+    it('should add Comfy-User header with plain object headers', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test', {
+        headers: {}
+      })
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.stringContaining('/test'),
+        expect.objectContaining({
+          headers: {
+            'Comfy-User': 'test-user'
+          }
+        })
+      )
+    })
+
+    it('should add Comfy-User header with Headers instance', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+      const headers = new Headers()
+
+      await api.fetchApi('/test', { headers })
+
+      expect(mockFetch).toHaveBeenCalled()
+      const callHeaders = mockFetch.mock.calls[0][1]?.headers
+      expect(callHeaders).toEqual(headers)
+    })
+
+    it('should add Comfy-User header with array headers', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+      const headers: [string, string][] = []
+
+      await api.fetchApi('/test', { headers })
+
+      expect(mockFetch).toHaveBeenCalled()
+      const callHeaders = mockFetch.mock.calls[0][1]?.headers
+      expect(callHeaders).toContainEqual(['Comfy-User', 'test-user'])
+    })
+
+    it('should preserve existing headers when adding Comfy-User', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test', {
+        headers: {
+          'Content-Type': 'application/json',
+          'X-Custom': 'value'
+        }
+      })
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.stringContaining('/test'),
+        expect.objectContaining({
+          headers: {
+            'Content-Type': 'application/json',
+            'X-Custom': 'value',
+            'Comfy-User': 'test-user'
+          }
+        })
+      )
+    })
+
+    it('should not allow developer-specified headers to be overridden by options', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test', {
+        headers: {
+          'Comfy-User': 'fennec-girl'
+        }
+      })
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.stringContaining('/test'),
+        expect.objectContaining({
+          headers: {
+            'Comfy-User': 'test-user'
+          }
+        })
+      )
+    })
+  })
+
+  describe('default options', () => {
+    it('should set cache to no-cache by default', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test')
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.any(String),
+        expect.objectContaining({
+          cache: 'no-cache'
+        })
+      )
+    })
+
+    it('should include required headers even when no headers option is provided', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test')
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.any(String),
+        expect.objectContaining({
+          headers: expect.objectContaining({
+            'Comfy-User': 'test-user'
+          })
+        })
+      )
+    })
+
+    it('should not override existing cache option', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test', { cache: 'force-cache' })
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.any(String),
+        expect.objectContaining({
+          cache: 'force-cache'
+        })
+      )
+    })
+  })
+
+  describe('URL construction', () => {
+    it('should use apiURL for route construction', async () => {
+      const mockFetch = vi
+        .mocked(global.fetch)
+        .mockResolvedValue(new Response())
+
+      await api.fetchApi('/test/route')
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.stringContaining('/api/test/route'),
+        expect.any(Object)
+      )
+    })
+  })
+})