The test should request the bandwidth that the user expected. This doesn't have to be the bandwidth they were actually (legally) promised, but what they understood they would get. This could be provided once for the Auto Test, and after each individual test. A default value could be stored in a user account, but the user would have to press a big button to confirm it each time. This would provide three possible types of values:
User Entered/Confirmed: xMbps
Profile default: xMbps
Last Entered/Confirmed: xMbps
I think this extra data is very useful.