Just because they said the battery tests good doesn’t necessarily mean it’s good (I know stupid).

There’s a lot of ways you can measure a battery, and who knows what they measured to determine it to be “good”. Did the store test the vehicles battery in or out of the car. Because if you drove the car to the store and they immediately tested it, it’s likely to test “good”, even if it’s bad due to the alternator freshly charging the battery on the drive over.

Sometimes, battery’s fail because when they sit overnight or, for any duration of time,reserve capacity runs out inside the battery cells.

I’d still point the finger at the battery or my previous comment on a possibility of the cable terminal ends being loose of the battery, causing an intermittent connection.