Gateway speed test

What's the best way to check internet speed at the gateway?   

If I understand correctly, xfinity speed test measures speed to the device.  On my xfinity app, the Internet Health/Check your Speeds seems to be non-functional.  (Not sure if this is because I have the gateway in bridge mode.  Doesn't seem like this would preclude speed measurement, but I've read conflicting posts on this.)  What's recommended?  

Thanks