iOS and Android users are familiar with the Speedtest application; actually, for many, it is the go-to source for determining your network and/or WiFi speeds while on your mobile (or tablet). Fortunately, owners of Windows Phone 8-powered devices can now join the party!
Following the source link you will be able to grab the new Speedtest app. It does what all its siblings do: determines the server closest to you after which it runs a download and then an upload test. Results are gathered together in a history list for easy reference. One word of note though: judging by the comments left on the application it appears that some owners of the Lumia 920 on AT&T are having issues running the program.
Source: Windows Phone Store