Update test_xcpp_kernel.py

Author: mcbarton

test/test_xcpp_kernel.py

@@ -248,7 +248,7 @@ class BaseXCppOpenMPTests(jupyter_kernel_test.KernelTests):
         def test_xcpp_omp(self):
             self.flush_channels()
             reply, output_msgs = self.execute_helper(code=self.omp_test_code, timeout=20)
-            output_text = ''.join(msg['content']['text'] for msg in stream_msgs)
+            output_text = ''.join(msg['content']['text'] for msg in output_msgs)
             thread_ids = set(map(int, re.findall(r'Hello from thread (\d+)', output_text)))
             expected_ids = set(range(4))
             self.assertEqual(thread_ids, expected_ids,f"Expected thread IDs {expected_ids}, but got {thread_ids}")