If you already have the 10440 cell, discharge it a little to get it down to 4.0V at least, then put a multimeter in series to measure current consumption between battery end and tail threads (Or wherever this light allows for battery-driver current measurement). If current consumption is above roughly 1A, best to immediately stop the test and conclude it is using too much power at 4V, let alone 4.2V.
If it isn't above 1A current, charge up battery the rest of the way and repeat the test, again much above 1A could be a problem and the test should be aborted.
If you have no Li-Ion cells to test with you could discharge a regular NiMH to ~ 1.0V/1.2v second test, and hold it in series with the CR123 cell to approximate the voltage of the above proposed tests... but as you wrote, they don't cost so much to be worried about but a working flashlight sure beats a dead one and the tests are pretty quick and easy.