private int unsignedToSigned(int unsigned, int size) {
        if ((unsigned & (1 << size - 1)) != 0) {
            unsigned = -1 * ((1 << size - 1) - (unsigned & ((1 << size - 1) - 1)));
        }
        return unsigned;
    }
Used for mocks and constants in rxandroidble, but instances created in mockrxandroidble, so the methods must be implemented
rxandroidble/src/test/java/android/bluetooth/BluetoothGattCharacteristic.java