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/platform/navigation/preservedQueryManager.test.ts

@@ -0,0 +1,73 @@
+import { beforeEach, describe, expect, it } from 'vitest'
+
+import {
+  capturePreservedQuery,
+  clearPreservedQuery,
+  hydratePreservedQuery,
+  mergePreservedQueryIntoQuery
+} from '@/platform/navigation/preservedQueryManager'
+import { PRESERVED_QUERY_NAMESPACES } from '@/platform/navigation/preservedQueryNamespaces'
+
+const NAMESPACE = PRESERVED_QUERY_NAMESPACES.TEMPLATE
+
+describe('preservedQueryManager', () => {
+  beforeEach(() => {
+    sessionStorage.clear()
+    clearPreservedQuery(NAMESPACE)
+  })
+
+  it('captures specified keys from the route query', () => {
+    capturePreservedQuery(NAMESPACE, { template: 'flux', source: 'custom' }, [
+      'template',
+      'source'
+    ])
+
+    hydratePreservedQuery(NAMESPACE)
+    const merged = mergePreservedQueryIntoQuery(NAMESPACE)
+
+    expect(merged).toEqual({ template: 'flux', source: 'custom' })
+    expect(sessionStorage.getItem('Comfy.PreservedQuery.template')).toBeTruthy()
+  })
+
+  it('hydrates cached payload from sessionStorage once', () => {
+    sessionStorage.setItem(
+      'Comfy.PreservedQuery.template',
+      JSON.stringify({ template: 'flux', source: 'default' })
+    )
+
+    hydratePreservedQuery(NAMESPACE)
+    const merged = mergePreservedQueryIntoQuery(NAMESPACE)
+
+    expect(merged).toEqual({ template: 'flux', source: 'default' })
+  })
+
+  it('merges stored payload only when query lacks the keys', () => {
+    capturePreservedQuery(NAMESPACE, { template: 'flux' }, ['template'])
+
+    const merged = mergePreservedQueryIntoQuery(NAMESPACE, {
+      foo: 'bar'
+    })
+
+    expect(merged).toEqual({ foo: 'bar', template: 'flux' })
+  })
+
+  it('returns undefined when merge does not change query', () => {
+    capturePreservedQuery(NAMESPACE, { template: 'flux' }, ['template'])
+
+    const merged = mergePreservedQueryIntoQuery(NAMESPACE, {
+      template: 'existing'
+    })
+
+    expect(merged).toBeUndefined()
+  })
+
+  it('clears cached payload', () => {
+    capturePreservedQuery(NAMESPACE, { template: 'flux' }, ['template'])
+
+    clearPreservedQuery(NAMESPACE)
+
+    const merged = mergePreservedQueryIntoQuery(NAMESPACE)
+    expect(merged).toBeUndefined()
+    expect(sessionStorage.getItem('Comfy.PreservedQuery.template')).toBeNull()
+  })
+})