Correct exception in from_dict

Signed-off-by: Pradyumna Krishna <[email protected]>

securesystemslib/metadata.py

@@ -3,7 +3,7 @@
 
 from typing import Any, List
 
-from securesystemslib import formats
+from securesystemslib import exceptions, formats
 from securesystemslib.signer import Signature
 from securesystemslib.util import b64dec, b64enc
 
@@ -56,7 +56,7 @@ def from_dict(cls, data: dict) -> "Envelope":
             KeyError: If any of the "payload", "payloadType" and "signatures"
                 fields are missing from the "data".
 
-            TypeError: If type of any signature in "signatures" is incorrect.
+            FormatError: If signature in "signatures" is incorrect.
 
         Returns:
             A "Envelope" instance.
@@ -74,9 +74,7 @@ def from_dict(cls, data: dict) -> "Envelope":
                 signatures.append(Signature.from_dict(signature))
 
             else:
-                raise TypeError(
-                    f"expected type 'Signature', got {type(signature).__name__}"
-                )
+                raise exceptions.FormatError("Wanted a 'Signature'.")
 
         return cls(payload, payload_type, signatures)
 

tests/test_metadata.py

@@ -3,9 +3,9 @@
 """Test cases for "metadata.py". """
 
 import copy
-from typing import Type
 import unittest
 
+from securesystemslib import exceptions
 from securesystemslib.metadata import Envelope
 from securesystemslib.signer import Signature
 
@@ -39,7 +39,7 @@ def test_envelope_from_to_dict(self):
 
         # Assert TypeError on invalid signature
         envelope_dict["signatures"] = [""]
-        self.assertRaises(TypeError, Envelope.from_dict, envelope_dict)
+        self.assertRaises(exceptions.FormatError, Envelope.from_dict, envelope_dict)
 
     def test_envelope_eq_(self):
         """Test envelope equality"""