Add a test for proper exception raising on bad start

Author: icook

bitcoin/tests/test_messages.py

@@ -114,6 +114,12 @@ def test_read_msg_verack(self):
         m = MsgSerializable.stream_deserialize(f)
         self.assertEqual(m.command, msg_verack.command)
 
+    def test_fail_invalid_message(self):
+        bad_verack_bytes = b'\xf8' + self.verackbytes[1:]
+        f = BytesIO(bad_verack_bytes)
+        with self.assertRaises(ValueError):
+            MsgSerializable.stream_deserialize(f)
+
     def test_msg_verack_to_bytes(self):
         m = msg_verack()
         b = m.to_bytes()