As in, 'I am about to murder my only son on your orders. If you are indeed the kind of god who would order me to do such a thing, then we'll see where that leaves us...'
That interpretation always struck me as truer to Old Testament tone.
Old Testament God is pretty firm on that line. :D
In short, it wasn’t really a test of either one, it was a public declaration that child sacrifice is bad.
Setting up a strawman for the kids would be par for the course though.
I'd say that argument has itself preemptively "retreat[ed] onto ever-shrinking intellectual turf. Defining God as something akin to the entire existence of the universe is something that essentially cannot be proved or disproved. Stick to that definition strictly, and yes there is nothing that an atheist can take logical issue with. But that strict definition also yields no conclusions/advice/insight either, so it's not very interesting. Hence seemingly no one ever being able to adopt such a definition and actually stick to it.