diff --git a/tests/storage/test_database.py b/tests/storage/test_database.py
new file mode 100644
index 0000000000..5a77c84962
--- /dev/null
+++ b/tests/storage/test_database.py
@@ -0,0 +1,52 @@
+# -*- 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.storage.database import make_tuple_comparison_clause
+from synapse.storage.engines import BaseDatabaseEngine
+
+from tests import unittest
+
+
+def _stub_db_engine(**kwargs) -> BaseDatabaseEngine:
+ # returns a DatabaseEngine, circumventing the abc mechanism
+ # any kwargs are set as attributes on the class before instantiating it
+ t = type(
+ "TestBaseDatabaseEngine",
+ (BaseDatabaseEngine,),
+ dict(BaseDatabaseEngine.__dict__),
+ )
+ # defeat the abc mechanism
+ t.__abstractmethods__ = set()
+ for k, v in kwargs.items():
+ setattr(t, k, v)
+ return t(None, None)
+
+
+class TupleComparisonClauseTestCase(unittest.TestCase):
+ def test_native_tuple_comparison(self):
+ db_engine = _stub_db_engine(supports_tuple_comparison=True)
+ clause, args = make_tuple_comparison_clause(db_engine, [("a", 1), ("b", 2)])
+ self.assertEqual(clause, "(a,b) > (?,?)")
+ self.assertEqual(args, [1, 2])
+
+ def test_emulated_tuple_comparison(self):
+ db_engine = _stub_db_engine(supports_tuple_comparison=False)
+ clause, args = make_tuple_comparison_clause(
+ db_engine, [("a", 1), ("b", 2), ("c", 3)]
+ )
+ self.assertEqual(
+ clause, "(a >= ? AND (a > ? OR (b >= ? AND (b > ? OR c > ?))))"
+ )
+ self.assertEqual(args, [1, 1, 2, 2, 3])
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