test: add failin WebSocket patching tests

test/browser/ws-api/ws.apply.browser.test.ts

@@ -12,7 +12,28 @@ declare global {
   }
 }
 
-test('does not apply the interceptor until "worker.start()" is called', async ({
+test('does not patch WebSocket class if no event handlers were defined', async ({
+  loadExample,
+  page,
+}) => {
+  await loadExample(require.resolve('./ws.runtime.js'), {
+    skipActivation: true,
+  })
+
+  await page.evaluate(async () => {
+    const { setupWorker } = window.msw
+    const worker = setupWorker()
+    await worker.start()
+  })
+
+  await expect(
+    page.evaluate(() => {
+      return new WebSocket('wss://example.com').constructor.name
+    }),
+  ).resolves.toBe('WebSocket')
+})
+
+test('does not patch WebSocket class until "worker.start()" is called', async ({
   loadExample,
   page,
 }) => {

test/node/ws-api/ws.apply.test.ts

@@ -0,0 +1,34 @@
+/**
+ * @vitest-environment node-websocket
+ */
+import { ws } from 'msw'
+import { setupServer } from 'msw/node'
+
+const server = setupServer()
+
+afterEach(() => {
+  server.close()
+})
+
+it('does not patch WebSocket class if no event handlers were defined', () => {
+  server.listen()
+
+  const raw = new WebSocket('wss://example.com')
+  expect(raw.constructor.name).toBe('WebSocket')
+  expect(raw).toBeInstanceOf(EventTarget)
+})
+
+it('does not patch WebSocket class until server.listen() is called', () => {
+  const api = ws.link('wss://example.com')
+  server.use(api.on('connection', () => {}))
+
+  const raw = new WebSocket('wss://example.com')
+  expect(raw.constructor.name).toBe('WebSocket')
+  expect(raw).toBeInstanceOf(EventTarget)
+
+  server.listen()
+
+  const mocked = new WebSocket('wss://example.com')
+  expect(mocked.constructor.name).not.toBe('WebSocket')
+  expect(mocked).toBeInstanceOf(EventTarget)
+})