test(pwa): M4 Task12 - PWA 分支单测（isDouyinUrl/resampleToMono/computeRms）

Author: Aparencia

client/src/features/classroom/capture/WebCaptureAdapter.test.ts

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+/**
+ * WebCaptureAdapter 纯函数测试（PWA 麦克风应急通道，M4 Task12 补测）
+ *
+ * @ai-context: 覆盖 resampleToMono（48k→16k 降采样 + 多声道混单）与
+ * computeRms（能量计算）。MediaRecorder/getUserMedia 依赖真实浏览器，
+ * jsdom 无法实例化，故仅测纯函数层。
+ * @ai-context EN: unit tests for resampleToMono (48k→16k downsampling +
+ * channel mixing) and computeRms. MediaRecorder/getUserMedia need a real
+ * browser, so only pure functions are covered under jsdom.
+ */
+import { describe, it, expect } from 'vitest';
+import { resampleToMono, computeRms } from './WebCaptureAdapter';
+
+/** 构造最小 AudioBuffer 假对象（仅覆盖 resampleToMono 用到的字段） */
+function fakeAudioBuffer(sampleRate: number, channelData: Float32Array[]): AudioBuffer {
+  return {
+    sampleRate,
+    numberOfChannels: channelData.length,
+    length: channelData[0]?.length ?? 0,
+    duration: 0,
+    getChannelData: (c: number) => channelData[c] ?? new Float32Array(0),
+  } as unknown as AudioBuffer;
+}
+
+describe('resampleToMono 重采样混单', () => {
+  it('48kHz 单声道降采样到 16kHz，长度约为 1/3', () => {
+    const src = new Float32Array(48000);
+    src.fill(0.5);
+    const out = resampleToMono(fakeAudioBuffer(48000, [src]), 16000);
+    expect(out.length).toBe(Math.floor(48000 / 3));
+    expect(out[0]).toBeCloseTo(0.5, 3);
+  });
+
+  it('双声道取平均', () => {
+    const left = new Float32Array(16000).fill(0.4);
+    const right = new Float32Array(16000).fill(0.8);
+    const out = resampleToMono(fakeAudioBuffer(16000, [left, right]), 16000);
+    expect(out.length).toBe(16000);
+    expect(out[0]).toBeCloseTo(0.6, 3);
+  });
+
+  it('空缓冲返回空数组', () => {
+    const out = resampleToMono(fakeAudioBuffer(48000, [new Float32Array(0)]), 16000);
+    expect(out.length).toBe(0);
+  });
+});
+
+describe('computeRms 能量计算', () => {
+  it('全零样本能量为 0', () => {
+    expect(computeRms(new Float32Array(100))).toBe(0);
+  });
+
+  it('满幅样本能量约为 1', () => {
+    const pcm = new Float32Array(100).fill(1.0);
+    expect(computeRms(pcm)).toBeCloseTo(1, 5);
+  });
+
+  it('空数组能量为 0', () => {
+    expect(computeRms(new Float32Array(0))).toBe(0);
+  });
+});

client/src/features/classroom/lib/uploadVideoAnalysis.test.ts

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+/**
+ * 视频上传分析工具纯函数测试（PWA 视频转笔记，M4 Task12 补测）
+ *
+ * @ai-context: 覆盖 isDouyinUrl 抖音链接检测（短链/长链/非抖音/非法 URL）。
+ * analyzeVideoFile 依赖真实 fetch + supabase，jsdom 覆盖收益低，留真机验证。
+ * @ai-context EN: unit tests for isDouyinUrl detection. analyzeVideoFile needs
+ * real fetch + supabase, left for device verification.
+ */
+import { describe, it, expect } from 'vitest';
+import { isDouyinUrl } from './uploadVideoAnalysis';
+
+describe('isDouyinUrl 抖音链接检测', () => {
+  it('识别 v.douyin.com 短链', () => {
+    expect(isDouyinUrl('https://v.douyin.com/AbCdEf/')).toBe(true);
+  });
+
+  it('识别 www.douyin.com 长链', () => {
+    expect(isDouyinUrl('https://www.douyin.com/video/123456789')).toBe(true);
+  });
+
+  it('无协议前缀返回 false（URL 解析失败不抛错）', () => {
+    expect(isDouyinUrl('v.douyin.com/xyz')).toBe(false);
+  });
+
+  it('拒绝非抖音域名', () => {
+    expect(isDouyinUrl('https://www.bilibili.com/video/123')).toBe(false);
+    expect(isDouyinUrl('https://douyin.evil.com/')).toBe(false);
+  });
+
+  it('拒绝非法 URL（不抛错）', () => {
+    expect(isDouyinUrl('')).toBe(false);
+    expect(isDouyinUrl('not a url')).toBe(false);
+  });
+});