feature: Multi-layer testing foundation — UI (fireEvent) + Electron (ElectronTestbed) test layers

[xerial]

Why

Goal: make Uni a foundation for building rich desktop apps testable at every layer, mirroring VSCode's testing strategy (unit → integration → UI/smoke → extension). Full roadmap: plans/2026-06-27-multi-layer-testing.md.

This branch delivers the two missing middle layers of that pyramid. Unit testing (UniTest) was already strong; this adds UI-interaction testing and Electron integration testing.

Layer 1 — UI (component) test toolkit wvlet.uni.dom.testing

Previously uni-dom tests could only renderTo and read textContent — no way to dispatch a click, keystroke, or input event. New, shipped in the published uni JS artifact:

• fireEvent — Testing-Library-style event simulation: click/dblclick/mouse, input/change/setChecked, keyDown/keyUp/keyPress (with modifiers), focus/blur, submit, custom.
• Query / TextMatcher — getBy/queryBy/queryAll for CSS selectors, data-testid, and element text (String or Regex); text queries return the deepest match.
• mount / Mounted — render an RxElement into a fresh container, query/interact via the handle, unmount() / AutoCloseable cleanup.
• DomTestSession + DomTestSupport (test scope) for automatic per-test cleanup via UniTest.after.

Tests run in real headless Chromium (Playwright): InteractionTest (clicks/typing/keyboard drive Rx state), QueryTest (query helpers). Full domTest suite green: 387 passed.

Layer 2 — Electron integration harness wvlet.uni.electron.testing.ElectronTestbed

In-memory Electron IPC harness so apps can integration-test RPC-over-IPC services without a real Electron runtime. Plays both sides of the IPC boundary (fake ipcMain + fake preload bridge), routing renderer requests to served routers through the full marshalling + RPCDispatcher path.

• API: ElectronTestbed.serve(routers*), .bridge(channel), .channelFactory(channel), .newAsyncClient.
• ElectronRPCTest now dogfoods it (hand-rolled fakeBridge removed).
• ElectronTestbedTest — stateful CounterApi integration test + unserved-channel error case. 7 electron tests passed.

Both toolkits ship in the published uni artifact (no test-framework dependency) so downstream desktop apps reuse them directly; only the UniTest-coupled DomTestSupport mixin is test-scope.

Roadmap (follow-up PRs)

1. UI test toolkit ✅ (this PR)
2. Electron integration harness ✅ (this PR)
3. UniTest test tags — select/exclude layers (unit/ui/electron) in CI
4. Plugin model + plugin test harness (needs design)

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive UI testing toolkit for uni-dom components, enabling real user interaction simulation and Testing-Library-style queries in headless browser environments. It includes event simulation via fireEvent, query helpers, and automated cleanup mechanisms. The review feedback highlights two key improvements: adding a null check for textContent in queryAllByText to prevent potential NullPointerException crashes in Scala.js, and refactoring cleanupMounted to safely pop elements from the collection to avoid concurrent modification issues if lifecycle hooks trigger additional mounts during teardown.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

In Scala.js, dom.Element.textContent can return null at runtime (e.g., for certain element types or in some headless DOM environments). If it returns null, passing it to matcher.matches will result in a NullPointerException because the default TextMatcher implementations call text.trim. Adding a null check prevents potential test suite crashes.

  def queryAllByText(matcher: TextMatcher): Seq[dom.Element] = 
    val all = queryAll("*").filter { e => 
      val txt = e.textContent 
      txt != null && matcher.matches(txt) 
    } 
    all.filterNot(e => all.exists(other => (other ne e) && e.contains(other)))

[gemini-code-assist]

Iterating over mountedElements using reverseIterator while calling m.unmount() can be unsafe if any component's lifecycle hooks (like beforeUnmount) trigger additional mounts, which would modify the mountedElements collection during iteration. Popping elements from the end of the ListBuffer in a while loop is safer, highly efficient, and naturally processes them in reverse order.

  /** Unmount every element mounted through this session, in reverse order. */
  def cleanupMounted(): Unit = 
    while mountedElements.nonEmpty do 
      val m = mountedElements.remove(mountedElements.size - 1) 
      try 
        m.unmount() 
      catch 
        case _: Throwable => 
          () // best-effort cleanup; never fail a test on teardown