tests: Improve verify_signature tests

Test unknown signature algorithm/scheme.

Also shorten the incorrect (but syntactically valid) signature a bit.

Signed-off-by: Jussi Kukkonen <[email protected]>

Author: Jussi Kukkonen

tests/test_api.py

@@ -205,6 +205,13 @@ def test_sign_verify(self):
         with self.assertRaises(exceptions.UnsignedMetadataError):
             targets_key.verify_signature(metadata_obj)
 
+        # Test failure on unknown scheme (securesystemslib UnsupportedAlgorithmError)
+        scheme = timestamp_key.scheme
+        timestamp_key.scheme = "foo"
+        with self.assertRaises(exceptions.UnsignedMetadataError):
+            timestamp_key.verify_signature(metadata_obj)
+        timestamp_key.scheme = scheme
+
         # Test failure on broken public key data (securesystemslib CryptoError)
         public = timestamp_key.keyval["public"]
         timestamp_key.keyval["public"] = "ffff"
@@ -220,7 +227,7 @@ def test_sign_verify(self):
             timestamp_key.verify_signature(metadata_obj)
 
         # Test failure with valid but incorrect signature
-        sig.signature = "52af76354db3403242e1437b1fbf1c7edc4e66b81dfd63b3026ff681d57e88e11a697cca78061a376a9dd8d7fde5777b14d4e6d8e75f976101cbc61321642f06"
+        sig.signature = "ff"*64
         with self.assertRaises(exceptions.UnsignedMetadataError):
             timestamp_key.verify_signature(metadata_obj)
         sig.signature = correct_sig