Fixed #3747 -- cache extensions on x.509 objects (#3769)

* Fixed #3747 -- cache extensions on x.509 objects

* be kind to cpython, save a dict lookup

* flake8

* changelog

1 files changed, 47 insertions, 0 deletions

diff --git a/tests/test_cryptography_utils.py b/tests/test_cryptography_utils.py
index 037d11cc..290e1612 100644
--- a/tests/test_cryptography_utils.py
+++ b/tests/test_cryptography_utils.py
@@ -4,8 +4,55 @@
 
 from __future__ import absolute_import, division, print_function
 
+import pytest
+
 from cryptography import utils
 
 
 def test_int_from_bytes_bytearray():
     assert utils.int_from_bytes(bytearray(b"\x02\x10"), "big") == 528
+
+
+class TestCachedProperty(object):
+    def test_simple(self):
+        accesses = []
+
+        class T(object):
+            @utils.cached_property
+            def t(self):
+                accesses.append(None)
+                return 14
+
+        assert T.t
+        t = T()
+        assert t.t == 14
+        assert len(accesses) == 1
+        assert t.t == 14
+        assert len(accesses) == 1
+
+        t = T()
+        assert t.t == 14
+        assert len(accesses) == 2
+        assert t.t == 14
+        assert len(accesses) == 2
+
+    def test_set(self):
+        accesses = []
+
+        class T(object):
+            @utils.cached_property
+            def t(self):
+                accesses.append(None)
+                return 14
+
+        t = T()
+        with pytest.raises(AttributeError):
+            t.t = None
+        assert len(accesses) == 0
+        assert t.t == 14
+        assert len(accesses) == 1
+        with pytest.raises(AttributeError):
+            t.t = None
+        assert len(accesses) == 1
+        assert t.t == 14
+        assert len(accesses) == 1