2 files changed, 20 insertions, 3 deletions
diff --git a/tests/hazmat/primitives/test_hkdf.py b/tests/hazmat/primitives/test_hkdf.py
index e3e2a9df..42c75c65 100644
--- a/tests/hazmat/primitives/test_hkdf.py
+++ b/tests/hazmat/primitives/test_hkdf.py
@@ -17,7 +17,9 @@ import six
 
 import pytest
 
-from cryptography.exceptions import AlreadyFinalized, InvalidKey
+from cryptography.exceptions import (
+    AlreadyFinalized, InvalidKey, UnsupportedInterface)
+
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.kdf.hkdf import HKDF
 
@@ -145,3 +147,10 @@ class TestHKDF(object):
             )
 
             hkdf.verify(b"foo", six.u("bar"))
+
+
+def test_invalid_backend():
+    pretend_backend = object()
+
+    with pytest.raises(UnsupportedInterface):
+        HKDF(hashes.SHA256(), 16, None, None, pretend_backend)
diff --git a/tests/hazmat/primitives/test_pbkdf2hmac.py b/tests/hazmat/primitives/test_pbkdf2hmac.py
index f895935b..a47d879e 100644
--- a/tests/hazmat/primitives/test_pbkdf2hmac.py
+++ b/tests/hazmat/primitives/test_pbkdf2hmac.py
@@ -18,8 +18,9 @@ import six
 
 from cryptography import utils
 from cryptography.exceptions import (
-    InvalidKey, UnsupportedHash, AlreadyFinalized
-)
+    InvalidKey, UnsupportedHash, AlreadyFinalized,
+    UnsupportedInterface)
+
 from cryptography.hazmat.primitives import hashes, interfaces
 from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
 from cryptography.hazmat.backends import default_backend
@@ -67,3 +68,10 @@ class TestPBKDF2HMAC(object):
         kdf = PBKDF2HMAC(hashes.SHA1(), 20, b"salt", 10, default_backend())
         with pytest.raises(TypeError):
             kdf.derive(six.u("unicode here"))
+
+
+def test_invalid_backend():
+    pretend_backend = object()
+
+    with pytest.raises(UnsupportedInterface):
+        PBKDF2HMAC(hashes.SHA1(), 20, b"salt", 10, pretend_backend)