There are some problems with using speedtest.net to indicate your ping in the broad sense. You can't actually troubleshoot ping issues this way.
The reasons for this are that:
- speedtest.net is only one website and your ping will differ to any point on the Internet, website or not.
- speedtest.net is hosted by a company and optimized to serve bandwidth. It is not a residential connection.
- People tend to pick locations that are closest to them on speedtest.net which gives them a distorted image of the realistic pings and bandwidth amounts. You're better off selecting a location that's half the country away or more to figure out more realistic pings/bandwidth.
- speedtest.net has an ISP as well. This ISP is not likely to be the same as the person(s) you're having issues with.
- ISPs may optimize speedtest.net (or other obvious mechanisms of testing) because they have an obvious interest in people believing that they're getting what they're paying for.
These things make it unsuitable as a general test of Internet connections. It is very difficult to troubleshoot Internet connections. There are some tools you can find that may aid in testing. There are also software applications.