Neilj/fix threepid auth check (with tests) (#4474)

test threepid checking

changelog.d/4474.misc

+Add test to verify threepid auth check added in #4435.

tests/config/test_server.py

+# -*- coding: utf-8 -*-
+# Copyright 2019 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.config.server import is_threepid_reserved
+
+from tests import unittest
+
+
+class ServerConfigTestCase(unittest.TestCase):
+
+    def test_is_threepid_reserved(self):
+        user1 = {'medium': 'email', 'address': 'user1@example.com'}
+        user2 = {'medium': 'email', 'address': 'user2@example.com'}
+        user3 = {'medium': 'email', 'address': 'user3@example.com'}
+        user1_msisdn = {'medium': 'msisdn', 'address': '447700000000'}
+        config = [user1, user2]
+
+        self.assertTrue(is_threepid_reserved(config, user1))
+        self.assertFalse(is_threepid_reserved(config, user3))
+        self.assertFalse(is_threepid_reserved(config, user1_msisdn))