Log saml assertions rather than the whole response

... since the whole response is huge.

We even need to break up the assertions, since kibana otherwise truncates them.

tests/util/test_itertools.py

@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# 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.util.iterutils import chunk_seq
+
+from tests.unittest import TestCase
+
+
+class ChunkSeqTests(TestCase):
+    def test_short_seq(self):
+        parts = chunk_seq("123", 8)
+
+        self.assertEqual(
+            list(parts), ["123"],
+        )
+
+    def test_long_seq(self):
+        parts = chunk_seq("abcdefghijklmnop", 8)
+
+        self.assertEqual(
+            list(parts), ["abcdefgh", "ijklmnop"],
+        )
+
+    def test_uneven_parts(self):
+        parts = chunk_seq("abcdefghijklmnop", 5)
+
+        self.assertEqual(
+            list(parts), ["abcde", "fghij", "klmno", "p"],
+        )
+
+    def test_empty_input(self):
+        parts = chunk_seq([], 5)
+
+        self.assertEqual(
+            list(parts), [],
+        )