test: add unit tests for ensurePlaywright auto-install logic

Tests cover: consumer resolution (fast path), auto-install when missing,
skip-install when cached, and Chromium browser installation.

Also adds a note to CLAUDE.md that features/fixes should include unit tests.

https://claude.ai/code/session_01XDxRzi588C73zsj1xPwmEb

Author: claude

CLAUDE.md

@@ -47,6 +47,9 @@ pnpm test           # all packages
 pnpm test --watch   # watch mode
 ```
 
+Features and bug fixes should include a unit test. Keep tests focused and avoid over-mocking —
+test the behaviour that matters, not implementation details.
+
 Integration tests require a running app. See `tests/integration/`.
 
 ## External-First Design Principle

tests/unit/ensure-playwright.test.ts

@@ -0,0 +1,141 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { join } from 'node:path';
+
+// Mock node:child_process
+vi.mock('node:child_process', () => ({
+  execFileSync: vi.fn(),
+}));
+
+// Mock node:fs — keep real join/path but control existsSync and readdirSync
+vi.mock('node:fs', async () => {
+  const actual = await vi.importActual<typeof import('node:fs')>('node:fs');
+  return {
+    ...actual,
+    existsSync: vi.fn(),
+    readdirSync: vi.fn(),
+  };
+});
+
+// Mock node:module — control createRequire
+vi.mock('node:module', () => ({
+  createRequire: vi.fn(),
+}));
+
+// Mock node:os
+vi.mock('node:os', () => ({
+  homedir: () => '/mock-home',
+  tmpdir: () => '/mock-tmp',
+}));
+
+import { existsSync, readdirSync } from 'node:fs';
+import { execFileSync } from 'node:child_process';
+import { createRequire } from 'node:module';
+import { ensurePlaywright } from '../../packages/core/src/recorder/ensure-playwright.js';
+
+const mockExistsSync = vi.mocked(existsSync);
+const mockReaddirSync = vi.mocked(readdirSync);
+const mockExecFileSync = vi.mocked(execFileSync);
+const mockCreateRequire = vi.mocked(createRequire);
+
+const fakePw = { chromium: { launch: vi.fn() } };
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.spyOn(console, 'info').mockImplementation(() => {});
+});
+
+describe('ensurePlaywright', () => {
+  it('returns playwright from consumer node_modules when available', async () => {
+    const fakeRequire = vi.fn().mockReturnValue(fakePw);
+    mockCreateRequire.mockReturnValue(fakeRequire as any);
+
+    const result = await ensurePlaywright();
+
+    expect(result).toBe(fakePw);
+    expect(mockCreateRequire).toHaveBeenCalledTimes(1);
+    expect(String(mockCreateRequire.mock.calls[0][0])).toContain('package.json');
+    // Should NOT run npm install
+    expect(mockExecFileSync).not.toHaveBeenCalled();
+  });
+
+  it('auto-installs when consumer does not have playwright', async () => {
+    const consumerRequire = vi.fn().mockImplementation(() => {
+      throw new Error('MODULE_NOT_FOUND');
+    });
+    const cacheRequire = vi.fn().mockReturnValue(fakePw);
+
+    mockCreateRequire
+      .mockReturnValueOnce(consumerRequire as any)
+      .mockReturnValueOnce(cacheRequire as any);
+
+    // Playwright package.json not yet in cache; Chromium is already present
+    mockExistsSync.mockImplementation((p) => {
+      const path = String(p);
+      if (path.includes('@playwright')) return false;
+      if (path.includes('ms-playwright')) return true;
+      return false;
+    });
+    mockReaddirSync.mockReturnValue(['chromium-1234'] as any);
+
+    const result = await ensurePlaywright();
+
+    expect(result).toBe(fakePw);
+    expect(mockExecFileSync).toHaveBeenCalledWith(
+      'npm',
+      expect.arrayContaining(['install', '@playwright/test']),
+      expect.objectContaining({ stdio: 'inherit' }),
+    );
+  });
+
+  it('skips npm install when playwright is already cached', async () => {
+    const consumerRequire = vi.fn().mockImplementation(() => {
+      throw new Error('MODULE_NOT_FOUND');
+    });
+    const cacheRequire = vi.fn().mockReturnValue(fakePw);
+
+    mockCreateRequire
+      .mockReturnValueOnce(consumerRequire as any)
+      .mockReturnValueOnce(cacheRequire as any);
+
+    // Everything already exists
+    mockExistsSync.mockReturnValue(true);
+    mockReaddirSync.mockReturnValue(['chromium-1234'] as any);
+
+    const result = await ensurePlaywright();
+
+    expect(result).toBe(fakePw);
+    // No npm install, no playwright install
+    expect(mockExecFileSync).not.toHaveBeenCalled();
+  });
+
+  it('installs chromium when browser cache is missing', async () => {
+    const consumerRequire = vi.fn().mockImplementation(() => {
+      throw new Error('MODULE_NOT_FOUND');
+    });
+    const cacheRequire = vi.fn().mockReturnValue(fakePw);
+
+    mockCreateRequire
+      .mockReturnValueOnce(consumerRequire as any)
+      .mockReturnValueOnce(cacheRequire as any);
+
+    const cacheDir = join('/mock-home', '.cache', 'git-glimpse', 'playwright');
+
+    mockExistsSync.mockImplementation((p) => {
+      const path = String(p);
+      // Package is installed but chromium cache doesn't exist
+      if (path.includes('@playwright')) return true;
+      if (path.includes('ms-playwright')) return false;
+      return false;
+    });
+
+    const result = await ensurePlaywright();
+
+    expect(result).toBe(fakePw);
+    // Should have called playwright install chromium
+    expect(mockExecFileSync).toHaveBeenCalledWith(
+      join(cacheDir, 'node_modules', '.bin', 'playwright'),
+      ['install', 'chromium', '--with-deps'],
+      expect.objectContaining({ stdio: 'inherit' }),
+    );
+  });
+});