'private_bytes' doesn't seem to exist for EC keys. So no good test.

Author: rohe

src/cryptojwt/jwk.py

@@ -410,7 +410,7 @@ def get_key(self, private=False):
         if not private and hasattr(self.key, 'public_key'):
             return self.key.public_key()
 
-        if private and not hasattr(self.key, 'private_bytes'):
+        if private and not self.is_private_key():
             raise ValueError("Not a private key")
 
         return self.key