Minor fixes
diff --git a/tests/hazmat/primitives/utils.py b/tests/hazmat/primitives/utils.py
index 7cf5efd..a496459 100644
--- a/tests/hazmat/primitives/utils.py
+++ b/tests/hazmat/primitives/utils.py
@@ -354,7 +354,7 @@
         backend=backend
     )
 
-    okm = hkdf._expand(binascii.unhexlify(params["prk"]))
+    okm = hkdf.derive(binascii.unhexlify(params["prk"]))
 
     assert okm == binascii.unhexlify(params["okm"])