diff --git a/tests/doubles.py b/tests/doubles.py
new file mode 100644
index 0000000..9dbb3ce
--- /dev/null
+++ b/tests/doubles.py
@@ -0,0 +1,41 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from cryptography import utils
+from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives.asymmetric import padding
+from cryptography.hazmat.primitives.ciphers import CipherAlgorithm
+from cryptography.hazmat.primitives.ciphers.modes import Mode
+
+
+@utils.register_interface(CipherAlgorithm)
+class DummyCipherAlgorithm(object):
+    name = "dummy-cipher"
+    block_size = 128
+    key_size = None
+
+
+@utils.register_interface(Mode)
+class DummyMode(object):
+    name = "dummy-mode"
+
+    def validate_for_algorithm(self, algorithm):
+        pass
+
+
+@utils.register_interface(hashes.HashAlgorithm)
+class DummyHashAlgorithm(object):
+    name = "dummy-hash"
+    block_size = None
+    digest_size = None
+
+
+@utils.register_interface(serialization.KeySerializationEncryption)
+class DummyKeySerializationEncryption(object):
+    pass
+
+
+@utils.register_interface(padding.AsymmetricPadding)
+class DummyAsymmetricPadding(object):
+    name = "dummy-padding"