Not sure if you are asking this because of ADSLMax's talking about downloading a 10GB file (although he used a lower case b which I suspect was an error) - the size of the file in that case would not be related to the line speed being tested.
So your speedtest supports 10 gigabit connections too?
I'm not aware of any speed tester that supports 10Gb connections. To do that you'd require a server with multiple 10Gb NIC ports that's running some kind of per-packet load balancing across them, and is supplied by a network with at least 10Gb of capacity available at all times.