"Battery Usage" page irrelevant
The BluetoothTest app is part of the stock image on most Samsung devices. It's a system app, and as the name suggests, it's for testing the Bluetooth hardware. If you root the device, it's safe to remove/"freeze" this app. It shouldn't normally run or cause any problems at all, though some users have reported that in some cases it shows up in the battery usage list for their device. (Googling {Samsung BluetoothTest} gives you some forum posts, but no solid information.)

As for the permission to "modify the battery statistics", this label is wrong (see this old Android bug report), and is phrased differently in newer Android versions. The permission only allows the app to read the battery statistics. An app might use this to help you identify which apps use the most power, or to find and disable power-hungry apps on low battery.

There's no real need for BluetoothTest to use this permission, but as the app info screen explains, many system apps are bound together in a single process, because this is more (power and memory) efficient. As a result, all of the apps bound together in this way share the same permissions, which means the single process has more permissions than any one of the apps needs. This only applies to system (i.e. built-in) apps: apps you download and install are kept separate for security.