Use a constant.

test/box/iproto.test.py

@@ -17,7 +17,7 @@ print """
 # Test bug #899343 (server assertion failure on incorrect packet)
 """
 print "# send the package with invalid length"
-inval_request = struct.pack('<LLL', 1, 4294967290, 1)
+inval_request = struct.pack('<LLL', box.net.SELECT, 4294967290, 1)
 print s.send(inval_request)
 print "# check that is server alive"
 sql("ping")