Add system test utility package isctest

Create a utility package for code shared by the python tests. The
utility functions should use reasonable defaults and be split up into
modules according to their functionality.

Ensure assert rewriting is enabled for the modules to get the most
useful output from pytest.

bin/tests/system/isctest/query.py

@@ -0,0 +1,35 @@
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+import os
+from typing import Optional
+
+import dns.query
+import dns.message
+
+
+QUERY_TIMEOUT = 10
+
+
+def udp(
+    message: dns.message.Message, ip: str, port: Optional[int] = None
+) -> dns.message.Message:
+    if port is None:
+        port = int(os.environ["PORT"])
+    return dns.query.udp(message, ip, QUERY_TIMEOUT, port=port)
+
+
+def tcp(
+    message: dns.message.Message, ip: str, port: Optional[int] = None
+) -> dns.message.Message:
+    if port is None:
+        port = int(os.environ["PORT"])
+    return dns.query.tcp(message, ip, QUERY_TIMEOUT, port=port)