How do I test running a GATT server in Linux?

Using the test scripts provided with BlueZ to setup a GATT server:

cd /lib/bluez/test/
./example-gatt-server &

Power on Bluetooth, start advertising and set to pairable:

# bluetoothctl
Agent registered
[bluetooth]# power on
Changing power on succeeded
[bluetooth]# advertise on
[bluetooth]# pairable on

Connect with Nordic's nRF smartphone app and read the fake battery level.