✅ Test WebSocket passthrough at the instrumentation layer

The collection layer only observes what webSocketObservable emits, so asserting
that application handlers and payloads survive belongs with the instrumentation.
Handler passthrough was already covered there; add the missing send-payload
case and drop the collection-level duplicate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: bdibon

packages/browser-core/src/browser/webSocketObservable.spec.ts

@@ -111,6 +111,16 @@ describe('webSocketObservable', () => {
         expect(customerHandler).toHaveBeenCalledTimes(1)
         expect(getContexts('closed').length).toBe(1)
       })
+
+      it('forwards the sent payload to the native send unaltered', () => {
+        const ws = createMockWebSocket('wss://example.com/socket')
+        const payload = 'hello'
+
+        ws.send(payload)
+
+        expect(ws.sentData).toEqual([payload])
+        expect(getContexts('message-out').length).toBe(1)
+      })
     })
 
     describe('open context', () => {

packages/browser-core/test/emulate/mockWebSocket.ts

@@ -38,6 +38,9 @@ export class MockWebSocket extends EventTarget {
   onmessage: ((event: MessageEvent) => void) | null = null
   onopen: ((event: Event) => void) | null = null
   onclose: ((event: CloseEvent) => void) | null = null
+  // Payloads that reached the socket, in order, so that specs can check instrumentation forwards
+  // them unaltered. Tests set `bufferedAmount` before calling send to verify it is sampled.
+  sentData: Array<string | ArrayBufferLike | Blob | ArrayBufferView> = []
 
   constructor(url: string | URL, protocols?: string | string[]) {
     super()
@@ -47,8 +50,8 @@ export class MockWebSocket extends EventTarget {
     }
   }
 
-  send(_data: string | ArrayBufferLike | Blob | ArrayBufferView): void {
-    // no-op; tests will set `bufferedAmount` before calling send to verify it is sampled.
+  send(data: string | ArrayBufferLike | Blob | ArrayBufferView): void {
+    this.sentData.push(data)
   }
 
   close(_code?: number, _reason?: string): void {

packages/browser-rum-core/src/domain/resource/webSocketCollection.spec.ts

@@ -667,32 +667,6 @@ describe('webSocketCollection', () => {
       })
     })
 
-    it('leaves application-set handlers and exchanged payloads untouched', () => {
-      const openHandler = jasmine.createSpy<(event: Event) => void>()
-      const messageHandler = jasmine.createSpy<(event: MessageEvent) => void>()
-      const closeHandler = jasmine.createSpy<(event: CloseEvent) => void>()
-      // spied before instrumentation is installed, so that the instrumented `send` delegates to it
-      const sendSpy = spyOn(window.WebSocket.prototype, 'send').and.callThrough()
-
-      startCollection()
-      const socket = notifyConnecting()
-      socket.onopen = openHandler
-      socket.onmessage = messageHandler
-      socket.onclose = closeHandler
-
-      notifyOpen(socket, 10)
-      setClock(20)
-      socket.simulateMessage('hello')
-      setClock(30)
-      socket.send('world')
-      notifyClosed(socket, 40, 1000, 'bye', true)
-
-      expect(openHandler).toHaveBeenCalledTimes(1)
-      expect(messageHandler.calls.mostRecent().args[0].data).toBe('hello')
-      expect(closeHandler.calls.mostRecent().args[0].code).toBe(1000)
-      expect(sendSpy).toHaveBeenCalledOnceWith('world')
-    })
-
     it('finalizes open connections with tracking_end_reason="session_end" when the session expires', () => {
       const endClocks = relativeToClocks(clock.relative(40))
       startCollection()