fix: exclude internal/computed fields that cause conflicts

Author: danceratopz

packages/testing/src/execution_testing/base_types/pydantic.py

@@ -35,9 +35,22 @@ def copy(self: Self, **kwargs: Any) -> Self:
         This method preserves the actual field values (including those set via
         default_factory) while maintaining the model_fields_set to track which
         fields were explicitly set.
+
+        The implementation uses exclude_unset=True as a safe baseline, then
+        explicitly adds back fields that were set via default_factory but not
+        explicitly set by the user. This avoids conflicts with models that have
+        mutually exclusive fields (e.g., Transaction with secret_key vs signature).
         """
-        # Get all current field values, including those set via default_factory
-        dump_dict = self.model_dump()
+        # Start with explicitly set fields (safe baseline)
+        dump_dict = self.model_dump(exclude_unset=True)
+
+        # For fields with default_factory, include them if they're not in model_fields_set
+        # This handles cases like Environment.gas_limit where the factory captures
+        # dynamic configuration that should be preserved in copies
+        for field_name, field_info in self.__class__.model_fields.items():
+            if field_name not in self.model_fields_set and field_info.default_factory:
+                dump_dict[field_name] = getattr(self, field_name)
+
         # Merge with the updates
         dump_dict.update(kwargs)
         # Create the new instance