👷 Migrate unit tests from Karma/Jasmine to Vitest by mormubis · Pull Request #4196 · DataDog/browser-sdk

mormubis · 2026-02-17T14:18:25Z

Motivation

Karma is deprecated. This migrates the full unit test suite to Vitest 4.x with browser mode (Playwright).

Changes

Most of the diff is mechanical spec file replacements (jasmine.createSpy() → vi.fn(), etc.). The interesting parts:

mockClock had to be rewritten because Vitest's vi.useFakeTimers fakes performance by default, which breaks every perf-related test. The toFake list now explicitly excludes it.

allJsonSchemas was using webpack's require.context to load schema files. Replaced with Vite's import.meta.glob.

BrowserStack needed bs-local.com as server host because Safari replaces localhost with its own domain, breaking cookie access in vitest's iframe. Same issue we already have with ServiceWorker tests in E2E. Cookie tests are still skipped on Safari because this alone doesn't fully fix it.

The unit-bs CI job needs Playwright installed with system deps (--with-deps) and 4 CPUs to handle 5 concurrent remote browsers without timing out.

vite@8.0.8 is pinned in the developer extension because @vitejs/plugin-react can't resolve vite/internal in newer patch versions.

3784 unit tests pass, 18628 BrowserStack tests across 5 browsers.

Test instructions

yarn test:unit
yarn typecheck
yarn lint

Checklist

Tested locally
Tested on staging
Added unit tests for this change.
Added e2e/integration tests for this change.
Updated documentation and/or relevant AGENTS.md file

github-actions · 2026-02-17T14:18:39Z

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

cit-pr-commenter-54b7da · 2026-02-17T15:57:28Z

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫%	Status
Rum	179.65 KiB	179.65 KiB	0.00%	✅
Rum Profiler	6.17 KiB	6.17 KiB	0.00%	✅
Rum Recorder	27.03 KiB	27.03 KiB	0.00%	✅
Logs	56.78 KiB	56.78 KiB	0.00%	✅
Rum Slim	135.50 KiB	135.50 KiB	0.00%	✅
Worker	23.63 KiB	23.63 KiB	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0039	0.0046	+17.95%
RUM - add action	0.0131	0.0142	+8.40%
RUM - add error	0.0117	0.0142	+21.37%
RUM - add timing	0.0025	0.0032	+28.00%
RUM - start view	0.0119	0.0141	+18.49%
RUM - start/stop session replay recording	0.0006	0.0009	+50.00%
Logs - log message	0.0138	0.0151	+9.42%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	31.78 KiB	30.88 KiB	-918 B
RUM - add action	56.94 KiB	56.51 KiB	-440 B
RUM - add timing	32.72 KiB	32.67 KiB	-58 B
RUM - add error	60.80 KiB	58.78 KiB	-2.02 KiB
RUM - start/stop session replay recording	32.10 KiB	31.67 KiB	-440 B
RUM - start view	484.29 KiB	481.56 KiB	-2.73 KiB
Logs - log message	95.66 KiB	94.06 KiB	-1.60 KiB

🔗 RealWorld

mormubis · 2026-05-05T15:04:31Z

+  },
+
+  test: {
+    browser: {


Browser mode with Playwright. Locally it runs headless Chromium. On BrowserStack, Playwright connects to remote browsers via WebSocket (wss://cdp.browserstack.com/playwright), so the old browser versions (Chrome 63, Edge 80, etc.) are real browsers hosted by BrowserStack, not local Playwright binaries. The aliases mirror tsconfig.base.json so vitest resolves packages the same way TypeScript does.

mormubis · 2026-05-05T15:04:40Z

+  // AND so performance.timing.navigationStart remains accessible.
+  // When performance IS faked, @sinonjs/fake-timers replaces the object and our
+  // override silently fails (the fake performance.now() starts at 0).
+  vi.useFakeTimers({


performance is excluded from toFake. If we fake it, performance.now() returns fake time but the browser's internal performance observer still uses real time. Breaks every perf-related test.

mormubis · 2026-05-05T15:04:42Z

+  mostRecent(): { args: Parameters<F>; returnValue: ReturnType<F> }
+}
+
+export function collectAsyncCalls<F extends (...args: any[]) => any>(


Vitest equivalent of the old Jasmine calls.all() pattern. Wraps a vi.fn() and resolves a promise once the expected number of calls is reached.

mormubis · 2026-05-05T15:04:43Z

+/// <reference types="vite/client" />
+// Load all JSON schema files from the rum-events-format submodule.
+// Uses Vite's import.meta.glob (replaces webpack's require.context).
+const schemaModules = import.meta.glob('../../../rum-events-format/schemas/**/*.json', { eager: true })


require.context → import.meta.glob. Same result, Vite API instead of webpack.

mormubis · 2026-05-05T15:05:02Z

+    browser: {
+      enabled: true,
+      provider: playwright(),
+      // Use bs-local.com instead of localhost so Safari on BrowserStack can access cookies.


Safari on BrowserStack replaces localhost with bs-local.com, which breaks cookie access in vitest's iframe. Same issue we already have with ServiceWorker tests in E2E.

mormubis · 2026-05-05T15:05:03Z

-      }, DOM_MUTATION_OBSERVABLE_DURATION)
-    }
+    return () =>
+      new Promise<void>((resolve) => {


Vitest doesn't support done() callbacks. Converted to new Promise<void>.

mormubis · 2026-05-05T15:05:05Z

 import { SESSION_STORE_KEY } from './sessionStoreStrategy'

+// Safari on BrowserStack cannot access cookies because vitest runs tests in an iframe
+// and BrowserStack replaces localhost with bs-local.com, triggering Safari's ITP restrictions.


Safari on BrowserStack still can't access cookies in the vitest iframe even with bs-local.com. Skipped on Safari only, runs fine on the other 4 browsers.

mormubis · 2026-05-05T15:05:06Z

@@ -1,3 +1,4 @@
+import { vi, beforeEach, describe, expect, it } from 'vitest'


Typical spec migration. jasmine.createSpy() → vi.fn(), spyOn → vi.spyOn, etc. All 257 spec files follow this same pattern.

trackRuntimeError: Add preventDefault() listeners to suppress Vitest's unhandled error reporting. Tests intentionally throw errors that are handled by the SDK's own onerror instrumentation, but Vitest also catches them via addEventListener. preventDefault() marks them as handled without blocking window.onerror. taskQueue: Snapshot requestSpy.mock.calls.length before iterating in callAllActiveCallbacks. Vitest's mock.calls array grows live (unlike Jasmine's calls.count() snapshot), so callbacks that trigger scheduleNextRun caused an infinite loop.

…bjectContaining)

…tions)

mormubis force-pushed the adlrb/vitest branch 5 times, most recently from 319576e to 02e30e1 Compare February 20, 2026 10:19

mormubis force-pushed the adlrb/vitest branch 18 times, most recently from 051c55a to 23d1a16 Compare April 30, 2026 21:16

mormubis added 4 commits May 5, 2026 12:34

👷 Add Vitest config, dependencies, and BrowserStack integration

ed5066a

👷 Add vitest CI jobs (unit-bs with Playwright and BrowserStack)

f6710f3

♻️ Migrate test utilities from Jasmine to Vitest

2ab9846

✅ Migrate 257 spec files from Jasmine to Vitest API

9f695e5

mormubis force-pushed the adlrb/vitest branch from e48694e to 9f695e5 Compare May 5, 2026 13:29

mormubis commented May 5, 2026

View reviewed changes

mormubis added 5 commits May 5, 2026 22:48

🎨 Fix formatting (Prettier)

40db9c0

🔀 Merge main and fix remaining Jasmine matchers (toBeFalse, jasmine.o…

5fa0433

…bjectContaining)

🎨 Fix lint errors from TypeScript 6.0.3 merge (unnecessary type asser…

0f02d49

…tions)

🎨 Fix formatting

c391085

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👷 Migrate unit tests from Karma/Jasmine to Vitest#4196

👷 Migrate unit tests from Karma/Jasmine to Vitest#4196
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		import { vi, beforeEach, describe, expect, it } from 'vitest'

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Checklist

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