Simplify InvalidLogoutToken exception

Remove the init overriding and use standard methods on the exception
object to examine it in the DecodeLogoutToken service unit tests.

Author: malcolmbaig

manage_breast_screening/auth/services.py

@@ -15,16 +15,6 @@
 class InvalidLogoutToken(Exception):
     """Raised when a CIS2 back-channel logout token is invalid."""
 
-    def __init__(self, cause=None):
-        """
-        Initialize with optional cause.
-
-        Args:
-            cause: The original exception that caused this error
-        """
-        self.cause = cause
-        super().__init__(str(cause) if cause else "Invalid logout token")
-
 
 class DecodeLogoutToken:
     def call(
@@ -68,4 +58,4 @@ def call(
             MissingClaimError,
         ) as e:
             logger.exception("Invalid logout token")
-            raise InvalidLogoutToken(cause=e) from e
+            raise InvalidLogoutToken() from e

manage_breast_screening/auth/tests/test_services.py

@@ -124,9 +124,8 @@ def test_invalid_claims_raise_error(
                 key_loader=self._key_loader(public_jwk),
             )
 
-        # Assert on the cause type and error message content
-        assert isinstance(excinfo.value.cause, expected_error_type)
-        assert expected_error_text in str(excinfo.value.cause)
+        assert isinstance(excinfo.value.__cause__, expected_error_type)
+        assert expected_error_text in str(excinfo.value.__cause__)
 
     def test_invalid_signature_raises_error(self):
         kid = "k1"
@@ -147,9 +146,8 @@ def test_invalid_signature_raises_error(self):
                 key_loader=self._key_loader(public_jwk_1),
             )
 
-        # Invalid signature should raise a JoseError
-        assert isinstance(excinfo.value.cause, JoseError)
-        assert "signature" in str(excinfo.value.cause).lower()
+        assert isinstance(excinfo.value.__cause__, JoseError)
+        assert "signature" in str(excinfo.value.__cause__)
 
     def test_expired_token_raises_error(self):
         kid = "k1"
@@ -173,10 +171,8 @@ def test_expired_token_raises_error(self):
                 client_id=client_id,
                 key_loader=self._key_loader(public_jwk),
             )
-
-        # Expired token should raise an ExpiredTokenError
-        assert isinstance(excinfo.value.cause, ExpiredTokenError)
-        assert "expired" in str(excinfo.value.cause).lower()
+        assert isinstance(excinfo.value.__cause__, ExpiredTokenError)
+        assert "expired" in str(excinfo.value.__cause__)
 
     def test_missing_iat_raises_error(self):
         kid = "k1"
@@ -197,6 +193,5 @@ def test_missing_iat_raises_error(self):
                 key_loader=self._key_loader(public_jwk),
             )
 
-        # Missing iat should raise a MissingClaimError
-        assert isinstance(excinfo.value.cause, MissingClaimError)
-        assert "iat" in str(excinfo.value.cause).lower()
+        assert isinstance(excinfo.value.__cause__, MissingClaimError)
+        assert "iat" in str(excinfo.value.__cause__)