The guy that wrote this test, Dan Elwell, says the web based tests can be inaccurate. He says
"Web-based Speed Tests use JavaScript technology to test speeds. JavaScript is great for web scripting, however when performing accurate work like testing speed it certainly has its disadvantages"
You can find the download speed and upload speed of your broadband by doing speed scan in http://www.scanmyspeed.com/ . Try the extended speed scan to get accurate speed test results.