Added backend check to hmac primitives

1 files changed, 16 insertions, 4 deletions

diff --git a/tests/hazmat/primitives/test_hmac.py b/tests/hazmat/primitives/test_hmac.py
index 88bed52c..24988e76 100644
--- a/tests/hazmat/primitives/test_hmac.py
+++ b/tests/hazmat/primitives/test_hmac.py
@@ -21,8 +21,10 @@ import six
 
 from cryptography import utils
 from cryptography.exceptions import (
-    AlreadyFinalized, UnsupportedHash, InvalidSignature
-)
+    AlreadyFinalized, UnsupportedHash, InvalidSignature,
+    UnsupportedInterface)
+
+from cryptography.hazmat.backends.interfaces import HMACBackend
 from cryptography.hazmat.primitives import hashes, hmac, interfaces
 
 from .utils import generate_base_hmac_test
@@ -52,8 +54,11 @@ class TestHMAC(object):
             h.update(six.u("\u00FC"))
 
     def test_copy_backend_object(self):
-        pretend_hmac = pretend.stub()
-        pretend_backend = pretend.stub(hmacs=pretend_hmac)
+        @utils.register_interface(HMACBackend)
+        class PretendBackend(object):
+            pass
+
+        pretend_backend = PretendBackend()
         copied_ctx = pretend.stub()
         pretend_ctx = pretend.stub(copy=lambda: copied_ctx)
         h = hmac.HMAC(b"key", hashes.SHA1(), backend=pretend_backend,
@@ -104,3 +109,10 @@ class TestHMAC(object):
     def test_unsupported_hash(self, backend):
         with pytest.raises(UnsupportedHash):
             hmac.HMAC(b"key", UnsupportedDummyHash(), backend)
+
+
+def test_invalid_backend():
+    pretend_backend = object()
+
+    with pytest.raises(UnsupportedInterface):
+        hmac.HMAC(b"key", hashes.SHA1(), pretend_backend)