feat(testing): test harness for @vue-tui/runtime

Provides render() for integration testing — async with auto-flush,
trimmed frames, fake terminal with resize(), stdin.write() with
auto-flush, and auto-cleanup via afterEach.

Exports: render, cleanup, RenderResult, RenderOptions, Terminal

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/testing/tests/render.test.tsx

@@ -0,0 +1,39 @@
+import { nextTick, ref } from "vue";
+import { expect, test } from "vite-plus/test";
+import { render } from "../src/index.ts";
+import { Text } from "@vue-tui/runtime";
+
+test("lastFrame captures rendered output", async () => {
+  const { lastFrame } = await render(() => <Text>hello</Text>);
+  expect(lastFrame()).toContain("hello");
+});
+
+test("frames accumulate on reactive updates", async () => {
+  const message = ref("first");
+  const { lastFrame, frames } = await render(() => <Text>{message.value}</Text>);
+  const initialCount = frames.length;
+  expect(lastFrame()).toContain("first");
+
+  message.value = "second";
+  await nextTick();
+  expect(lastFrame()).toContain("second");
+  expect(frames.length).toBeGreaterThan(initialCount);
+});
+
+test("render with custom columns", async () => {
+  const { lastFrame } = await render(() => <Text>hello</Text>, { columns: 20 });
+  expect(lastFrame()).toContain("hello");
+});
+
+test("lastFrame trims trailing whitespace", async () => {
+  const { lastFrame } = await render(() => <Text>hi</Text>);
+  const frame = lastFrame()!;
+  for (const line of frame.split("\n")) {
+    expect(line).toBe(line.trimEnd());
+  }
+});
+
+test("auto cleanup — no manual unmount needed", async () => {
+  const { lastFrame } = await render(() => <Text>auto</Text>);
+  expect(lastFrame()).toContain("auto");
+});

packages/testing/tests/streams.test.ts

@@ -0,0 +1,23 @@
+import { expect, test } from "vite-plus/test";
+import { makeFakeStdin, makeFakeWritable } from "../src/streams.ts";
+
+test("fake stdout reports columns/rows and isTTY", () => {
+  const s = makeFakeWritable({ columns: 50, rows: 10 });
+  expect(s.columns).toBe(50);
+  expect(s.rows).toBe(10);
+  expect(s.isTTY).toBe(true);
+});
+
+test("fake stdin supports setRawMode and emits data", () => {
+  const { stream: s, rawMode } = makeFakeStdin();
+  expect(s.isTTY).toBe(true);
+  let observed = "";
+  s.on("data", (c) => {
+    observed += c.toString();
+  });
+  s.setRawMode(true);
+  expect(rawMode.current).toBe(true);
+  expect(rawMode.history).toEqual([true]);
+  s.emit("data", "hello");
+  expect(observed).toBe("hello");
+});