Device Diagnostics Beta is a useful application for Nokia Symbian touch phones which helps you to test several features of your phone.
Following are some of the available diagnostics tests:

Network Coverage Test: Checks the current signal strength, Operator info,  presence of SIM card, offline profile and roaming status.
Internet Connectivity Test: Checks the internet access settings on the device and identifies the working settings for seamless internet access. If no settings are found, the test updates the device with new settings based on current service provider.
Battery Charger Test: Checks if the charger is connected and whether the device charges properly.

Earpiece Test: Plays Nokia ringing tone over the earpience.

Loudspeaker Test: Plays Nokia ringing tone over the speaker.