refactor: reduce code duplication in vehicle response handling

dvsa_mot_history/client.py

@@ -78,47 +78,36 @@ async def _make_api_request(self, url: str) -> Union[Dict[str, Any], ErrorRespon
                     status_code=response.status, message="Unknown error", errors=None
                 )
 
-    async def get_vehicle_history_by_registration(
-        self, registration: str
+    async def _process_vehicle_history_response(
+        self, response_json: Dict[str, Any] | ErrorResponse
     ) -> Union[VehicleWithMotResponse, NewRegVehicleResponse, ErrorResponse]:
-        """Get MOT history for a vehicle by registration."""
-        url = build_url(VEHICLE_BY_REGISTRATION, registration=registration)
-        response_json = await self._make_api_request(url)
-
+        """Process the vehicle history response."""
         if isinstance(response_json, ErrorResponse):
             return response_json
 
-        classified_response: Union[VehicleWithMotResponse, NewRegVehicleResponse]
-
-        if hasattr(response_json, "motTests"):
+        if "motTests" in response_json:
             response_json["motTests"] = await try_cast_mot_class(response_json)
-            classified_response = VehicleWithMotResponse(**response_json)
+            return VehicleWithMotResponse(**response_json)
+        elif "motTestDueDate" in response_json:
+            return NewRegVehicleResponse(**response_json)
 
-        else:
-            classified_response = NewRegVehicleResponse(**response_json)
+        raise ValueError("Unexpected response format")
 
-        return classified_response
+    async def get_vehicle_history_by_registration(
+        self, registration: str
+    ) -> Union[VehicleWithMotResponse, NewRegVehicleResponse, ErrorResponse]:
+        """Get MOT history for a vehicle by registration."""
+        url = build_url(VEHICLE_BY_REGISTRATION, registration=registration)
+        response_json = await self._make_api_request(url)
+        return await self._process_vehicle_history_response(response_json)
 
     async def get_vehicle_history_by_vin(
         self, vin: str
     ) -> Union[VehicleWithMotResponse, NewRegVehicleResponse, ErrorResponse]:
         """Get MOT history for a vehicle by VIN."""
         url = build_url(VEHICLE_BY_VIN, vin=vin)
         response_json = await self._make_api_request(url)
-
-        if isinstance(response_json, ErrorResponse):
-            return response_json
-
-        classified_response: Union[VehicleWithMotResponse, NewRegVehicleResponse]
-
-        if hasattr(response_json, "motTests"):
-            response_json["motTests"] = await try_cast_mot_class(response_json)
-            classified_response = VehicleWithMotResponse(**response_json)
-
-        else:
-            classified_response = NewRegVehicleResponse(**response_json)
-
-        return classified_response
+        return await self._process_vehicle_history_response(response_json)
 
     async def get_bulk_download(self) -> Union[BulkDownloadResponse, ErrorResponse]:
         """Get MOT history in bulk."""