This is true of most internet speed tests though. Even speedtest.net uses their own servers. If you're measuring for speed you just need to be sure that the server has higher bandwidth available than your ISP.
If you're looking for a generic internet connectivity test then you'll need to test a few dozen sites at least, with diversity in which CDN's they're using and so on.
If you're looking for a generic internet connectivity test then you'll need to test a few dozen sites at least, with diversity in which CDN's they're using and so on.