Geo-location testing is performed on apps that are location-aware, meaning display/collect information based on the current location of the device.

At, Geo-Location testing is performed in a manner similar to field testing, except it is much more easier. It is done by simply choosing a location of choice on a virtual map, which internally feeds lat/long information to the device. It is as if the device is present at your chosen location. This will help you to test if your application behaves properly at different locations. 

Please note that the operator, network, temperature, language etc will remain same as the device's original location.