You can do a free battery test on your own. Turn the key and if the voltage drops the battery is defective.at assumes it has been on charge for a long time so it is not just a bit flat. The stater motor is acting as the drop tester.
True Frank to a degree however, this is not a 'stalled' starter so the results will not be accurate. Once the engine starts to spin the 'load' on the batteries falls. A fixed load is needed to get an accurate reading, this topic can go around and around but the outcome will always be the same, a known fixed load is the only way to get a genuine and guaranteed test of a car battery.