Hello Paul,
Battery test sounds like a voltmeter testing the alternator output voltage and the voltage at the battery with lights on etc. Ok, but..... the ultimate tests are if the battery is able to retain the charge which is put into it, and be able to efficiently produce the high current demand placed in it when starting -while maintaining an acceptable voltage.
Halfords normally carry out battery testing and are able to give you a % efficiency reading which will firmly point you to whether the battery is as serviceable as it should be. If you do eventually have it tested and if it does need replacing, you can then decide where you will get one from.
As you say, you don't want to buy a new battery, and I wouldn't too, so let's hope it all works out in the end.
Kind regards,
Gareth.