[v0.41.0-alpha.3] Candidate 3: Consolidate the Test DOM Harness

[SisyphusZheng]

From architecture review improve-codebase-architecture. Deferred ponytail debt from alpha.2 bot reviews.

Problem

Fake DOM infrastructure (TestEvent, TestElement, TestShadowRoot, TestDocument, withMockDocument, flushRaf) is repeated across several large test files (binding-activation.test.ts, hydration-scope.test.ts, jsx-render-dom.test.ts, open-element.test.ts, components.test.ts). Subtle fake-DOM differences can hide browser-like bugs.

Solution

Create one internal test-support module (packages/core/__tests__/test-utils.ts already exists) that owns fake DOM construction, event dispatch, shadow root setup, and cleanup. Extract common classes and helpers.

Files/modules

packages/core/__tests__/test-utils.ts, binding-activation.test.ts, hydration-scope.test.ts, jsx-render-dom.test.ts, packages/element/__tests__/open-element.test.ts, packages/ui/__tests__/components.test.ts

Priority

Worth exploring — low complexity, high test-quality impact.

[SisyphusZheng]

Closing as completed by the alpha.3 release PR #110, whose release notes list #109 as completed and explicitly say "Closes #107, #108, #109": #110