From 7fa71e32670aa0ed2b49d04fd3c66a72e8fbc1cf Mon Sep 17 00:00:00 2001
From: Mark Haines <mark.haines@matrix.org>
Date: Wed, 23 Dec 2015 11:48:03 +0000
Subject: [PATCH] Add a unit test for the snapshot cache

---
 synapse/util/caches/snapshot_cache.py |  4 +-
 tests/util/test_snapshot_cache.py     | 60 +++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 tests/util/test_snapshot_cache.py

diff --git a/synapse/util/caches/snapshot_cache.py b/synapse/util/caches/snapshot_cache.py
index b19aca05a..8a7ca47a8 100644
--- a/synapse/util/caches/snapshot_cache.py
+++ b/synapse/util/caches/snapshot_cache.py
@@ -28,14 +28,14 @@ class SnapshotCache(object):
 
     def rotate(self, time_now_ms):
         # Rotate once if the cache duration has passed since the last rotation.
-        if time_now_ms - self.time_last_rotated_ms > self.DURATION_MS:
+        if time_now_ms - self.time_last_rotated_ms >= self.DURATION_MS:
             self.prev_result_cache = self.next_result_cache
             self.next_result_cache = {}
             self.time_last_rotated_ms += self.DURATION_MS
 
         # Rotate again if the cache duration has passed twice since the last
         # rotation.
-        if time_now_ms - self.time_last_rotated_ms > self.DURATION_MS:
+        if time_now_ms - self.time_last_rotated_ms >= self.DURATION_MS:
             self.prev_result_cache = self.next_result_cache
             self.next_result_cache = {}
             self.time_last_rotated_ms = time_now_ms
diff --git a/tests/util/test_snapshot_cache.py b/tests/util/test_snapshot_cache.py
new file mode 100644
index 000000000..f58576c94
--- /dev/null
+++ b/tests/util/test_snapshot_cache.py
@@ -0,0 +1,60 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 OpenMarket 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 .. import unittest
+
+from synapse.util.caches.snapshot_cache import SnapshotCache
+from twisted.internet.defer import Deferred
+
+class SnapshotCacheTestCase(unittest.TestCase):
+
+    def setUp(self):
+        self.cache = SnapshotCache()
+        self.cache.DURATION_MS = 1
+
+    def test_get_set(self):
+        # Check that getting a missing key returns None
+        self.assertEquals(self.cache.get(0, "key"), None)
+
+        # Check that setting a key with a deferred returns
+        # a deferred that resolves when the initial deferred does
+        d = Deferred()
+        set_result = self.cache.set(0, "key", d)
+        self.assertIsNotNone(set_result)
+        self.assertFalse(set_result.called)
+
+        # Check that getting the key before the deferred has resolved
+        # returns a deferred that resolves when the initial deferred does.
+        get_result_at_10 = self.cache.get(10, "key")
+        self.assertIsNotNone(get_result_at_10)
+        self.assertFalse(get_result_at_10.called)
+
+        # Check that the returned deferreds resolve when the initial deferred
+        # does.
+        d.callback("v")
+        self.assertTrue(set_result.called)
+        self.assertTrue(get_result_at_10.called)
+
+        # Check that getting the key after the deferred has resolved
+        # before the cache expires returns a resolved deferred.
+        get_result_at_11 = self.cache.get(11, "key")
+        self.assertIsNotNone(get_result_at_11)
+        self.assertTrue(get_result_at_11.called)
+
+        # Check that getting the key after the deferred has resolved
+        # after the cache expires returns None
+        get_result_at_12 = self.cache.get(12, "key")
+        self.assertIsNone(get_result_at_12)