I believe SpeedTest.net is by far the most widely known and used internet speed checker on the web. However, many indian ISPs know this as well and they often go through extra efforts to "fudge" the numbers that their customers get from SpeedTest.net.
This is my experience with YOU broadband. I am on the 10 Mbps plan since 1 month. On testing the download speed on speedtest.net I mostly see around 4-5 Mbps, but whenever I actually downlaod something I never get beyond 400Kbps ie 50KBps
After a bit of research and doing the download test on other websites (google "download speed test") I realised that YOU broadband is allowing all traffic to/from speedtest.net at maximum bandwidth to give an impression of higher download speeds to its customers. In reality the bandwidtha dn download speeds that users/customers get is much lower.
The technician who visited my house did not have any answers when I asked him this. In the end he only said that most other ISPs in India do the same and it is easy since everyone uses speedtest.net to check their download speeds.
I suggest you always try to get at least 2 results for an unbiased view of your internet speed. If they are around the same you can be quite sure of the results otherwise try with the third.
Please try it for yourselves and let others know this.
PS. Also posted on mouth shut.