fix: forward server errors to WebSocket client (#507)

src/interceptors/WebSocket/WebSocketServerConnection.ts

@@ -117,6 +117,14 @@ export class WebSocketServerConnection {
       this.transport.onIncoming(event)
     })
 
+    // Forward server errors to the WebSocket client as-is.
+    // We may consider exposing them to the interceptor in the future.
+    ws.addEventListener('error', () => {
+      this.mockWebSocket.dispatchEvent(
+        bindEvent(this.mockWebSocket, new Event('error'))
+      )
+    })
+
     this.realWebSocket = ws
   }
 

test/modules/WebSocket/exchange/websocket.server.connect.test.ts

@@ -1,7 +1,7 @@
 /**
  * @vitest-environment node-with-websocket
  */
-import { it, expect, beforeAll, afterEach, afterAll } from 'vitest'
+import { vi, it, expect, beforeAll, afterEach, afterAll } from 'vitest'
 import { WebSocketServer } from 'ws'
 import { DeferredPromise } from '@open-draft/deferred-promise'
 import { WebSocketInterceptor } from '../../../../src/interceptors/WebSocket'
@@ -104,3 +104,17 @@ it('closes the actual server connection when the client closes', async () => {
   expect(ws.readyState).toBe(WebSocket.CLOSED)
   expect(realWebSocket?.readyState).toBe(WebSocket.CLOSING)
 })
+
+it('throw an error when connecting to a non-existing server', async () => {
+  interceptor.once('connection', ({ server }) => {
+    server.connect()
+  })
+
+  const errorListener = vi.fn()
+  const ws = new WebSocket('ws://localhost:9876')
+  ws.onerror = errorListener
+
+  await vi.waitFor(() => {
+    expect(errorListener).toHaveBeenCalledTimes(1)
+  })
+})