While some ISPs offer their own speed tests, most that I've used do not; and, there is, of course, always the concern as to the accuracy of test provider by a supplier.
And, there are independent sites that offer such; but, such are not well known to all, some are difficult to understand and use, and, some queue your request.
So, what's to lose by trying a new one; and, help the FCC get a better picture of just how who's getting what where.
Before trying the test located at Welcome to Broadband.gov , you might want to first read the following articles.
FCC Offers Free Broadband Speed Test : PC World
FCC Launches Broadband Test Site for Consumers : PC World