Well, you can test robot_localization, but if you are using logged GPS data with live IMU data, it's not going to be pretty. The robot's motion when the GPS data was collected will almost certainly not align with the IMU's orientation over time, so the output will be a little strange.
That said, if you just want to make sure everything is flowing, then I'd suggest writing a new node that reads your GPS data from a file and publishes a sensor_msgs/NavSatFix message with the required data. You'll also need to use navsat_transform_node.