👷 Add vitest.bs.config.ts for BrowserStack unit tests

Creates the Vitest BrowserStack config required by the 'unit-bs' CI job.
Mirrors karma.bs.conf.js: uses @vitest/browser-playwright with connectOptions
to route each browser session through BrowserStack's CDP endpoint.

Also fixes startRum.spec.ts flaky tests: use vi.setSystemTime(navigationStart
+ VIEW_DURATION) instead of clock.tick(VIEW_DURATION - relativeNow()) to
advance the clock to the correct absolute time without risk of negative ticks.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: mormubis

eslint.config.mjs

@@ -469,7 +469,7 @@ export default tseslint.config(
   },
 
   {
-    files: ['**/webpack.*.{ts,mts}', 'eslint-local-rules/**/*.js', 'vitest.config.ts'],
+    files: ['**/webpack.*.{ts,mts}', 'eslint-local-rules/**/*.js', 'vitest.config.ts', 'vitest.bs.config.ts'],
     rules: {
       // Webpack configuration files, eslint rules files, and vitest config are expected to use a default export.
       'import/no-default-export': 'off',
@@ -484,6 +484,7 @@ export default tseslint.config(
       'packages/*/test/**/*.ts',
       'test/unit/**/*.ts',
       'vitest.config.ts',
+      'vitest.bs.config.ts',
     ],
     rules: {
       // E2E, test utilities, and spec files import packages referenced by tsconfig or root devDependencies (vitest).

vitest.bs.config.ts

@@ -0,0 +1,113 @@
+import path from 'node:path'
+
+import { playwright } from '@vitest/browser-playwright'
+import { defineConfig } from 'vitest/config'
+
+// eslint-disable-next-line local-rules/disallow-test-import-export-from-src
+import { getBuildInfos } from './test/envUtils.ts'
+// eslint-disable-next-line local-rules/disallow-test-import-export-from-src
+import { browserConfigurations } from './test/unit/browsers.conf.ts'
+import packageJson from './package.json' with { type: 'json' }
+
+// Build env variables that should be replaced at compile time (same as webpack.base.ts)
+const buildEnvDefines: Record<string, string> = {
+  __BUILD_ENV__SDK_VERSION__: JSON.stringify('test'),
+  __BUILD_ENV__SDK_SETUP__: JSON.stringify('npm'),
+  // Worker string is built from packages/worker — provide empty string for unit tests
+  __BUILD_ENV__WORKER_STRING__: JSON.stringify(''),
+}
+
+function getPlaywrightBrowserName(name: string): 'chromium' | 'firefox' | 'webkit' {
+  if (name.toLowerCase().includes('firefox')) {
+    return 'firefox'
+  }
+  if (name.toLowerCase().includes('safari') || name.toLowerCase().includes('webkit')) {
+    return 'webkit'
+  }
+  return 'chromium'
+}
+
+function getCapabilities(configuration: (typeof browserConfigurations)[number]) {
+  const rootPkg = packageJson as unknown as { devDependencies?: Record<string, string> }
+  const playwrightVersion = rootPkg.devDependencies?.['@playwright/test'] ?? 'latest'
+  return {
+    os: configuration.os,
+    os_version: configuration.osVersion,
+    browser: configuration.name,
+    browser_version: configuration.version,
+    'browserstack.username': process.env.BS_USERNAME,
+    'browserstack.accessKey': process.env.BS_ACCESS_KEY,
+    project: 'browser sdk unit',
+    build: getBuildInfos(),
+    name: configuration.sessionName,
+    'browserstack.local': true,
+    'browserstack.playwrightVersion': playwrightVersion,
+    'client.playwrightVersion': playwrightVersion,
+    'browserstack.debug': false,
+    'browserstack.console': 'info',
+    'browserstack.networkLogs': false,
+    'browserstack.interactiveDebugging': false,
+  }
+}
+
+export default defineConfig({
+  resolve: {
+    alias: {
+      // Test utility subpath imports (must come before main package aliases)
+      '@datadog/browser-core/test': path.resolve('./packages/core/test'),
+      '@datadog/browser-rum-core/test': path.resolve('./packages/rum-core/test'),
+
+      // Main package aliases (matching tsconfig.base.json paths)
+      '@datadog/browser-core': path.resolve('./packages/core/src'),
+      '@datadog/browser-flagging': path.resolve('./packages/flagging/src/entries/main'),
+      '@datadog/browser-logs': path.resolve('./packages/logs/src/entries/main'),
+      '@datadog/browser-rum-core': path.resolve('./packages/rum-core/src'),
+      '@datadog/browser-rum/internal': path.resolve('./packages/rum/src/entries/internal'),
+      '@datadog/browser-rum/internal-synthetics': path.resolve('./packages/rum/src/entries/internalSynthetics'),
+      '@datadog/browser-rum': path.resolve('./packages/rum/src/entries/main'),
+      '@datadog/browser-rum-slim': path.resolve('./packages/rum-slim/src/entries/main'),
+      '@datadog/browser-rum-react/react-router-v6': path.resolve('./packages/rum-react/src/entries/reactRouterV6'),
+      '@datadog/browser-rum-react/react-router-v7': path.resolve('./packages/rum-react/src/entries/reactRouterV7'),
+      '@datadog/browser-rum-react': path.resolve('./packages/rum-react/src/entries/main'),
+      '@datadog/browser-worker': path.resolve('./packages/worker/src/entries/main'),
+    },
+  },
+
+  define: buildEnvDefines,
+
+  optimizeDeps: {
+    include: ['pako'],
+  },
+
+  test: {
+    browser: {
+      enabled: true,
+      provider: playwright(),
+      instances: browserConfigurations.map((config) => ({
+        browser: getPlaywrightBrowserName(config.name),
+        playwright: {
+          connectOptions: {
+            wsEndpoint: `wss://cdp.browserstack.com/playwright?caps=${encodeURIComponent(JSON.stringify(getCapabilities(config)))}`,
+          },
+        },
+      })),
+    },
+
+    // Exclude developer-extension: only compatible with Chrome, no point testing on other browsers
+    include: ['packages/*/{src,test}/**/*.spec.{ts,tsx}'],
+
+    exclude: [
+      'packages/core/src/domain/error/trackRuntimeError.spec.ts',
+      'packages/core/src/tools/taskQueue.spec.ts',
+      '**/node_modules/**',
+    ],
+
+    restoreMocks: true,
+
+    setupFiles: ['./test/unit/vitest.setup.ts'],
+
+    sequence: {
+      shuffle: true,
+    },
+  },
+})