To make a load for "low" to-moderate currents you can get power resistors and optionally wire them in parallel (or series-parallel).
Or maybe just turning-on the headlights is enough of a load to get a useful measurement?
If you want to simulate starting current you might be able to make your own load resistor with nichrome wire. Otherwise you'll need to by a proper automotive battery load tester.
A quick search says starting current is usually 400-1000A. 500Amps at 12V is 6 kilowatts and that's a BIG resistor! But it's not impossible... A toaster or hair drier is basically a ~1kW resistor. And, the voltage will drop, so that's less wattage, and you'd only be testing for a few (or several) seconds so the resistor doesn't have to handle the power for very long.
Of course, load testing drains the battery... So maybe it would start but you're on the "hairy edge" but after testing there isn't enough charge to start.
If you want to measure current, a hall-effect current sensor is the best way to measure high current.
I don't know the test conditions (temperature or time-duration) but batteries can't put-out as much current when cold, so this is supposed to be a "worst case" test of how the battery will perform in cold weather/climates.
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...A couple of months ago I thought I had a dead battery. The engine was turning-over slowly. I called AAA and the tow truck driver had a little palm sized gizmo that he hooked-up and it communicates with his phone. It was weird because the battery was only about a year old. But he sold me a new battery and the car started right-up. Then about a week later, same problem... Slow to turn-over and wouldn't start. I was at home so I checked the voltage and it was a little low but it didn't seem too bad. I put a charger on it and a couple of hours later it started fine.
I have an adapter-plug that plugs into the car's "cigarette lighter" so I hooked-up my meter to monitor what was going-on. The voltage seemed to be holding-up so the charging system was working but a week later, same thing again. I came out of a store and it wouldn't start. This time, the AAA driver couldn't jump-start it. (He didn't tell me what his tester was showing.) He (correctly) guessed it was the starter and he banged-on the starter with a rod. (The starter is behind the intake manifold and it's hard to get-to). Amazingly, the car started and I drove it straight to the mechanic. He replaced the starter and everything has been good.
In the meantime, I bought a little USB adapter that has a voltage display (it displays the 12V 'input" voltage) so I can keep an eye on things. Then I bought another one. My other vehicle has a analog voltmeter but it's not marked "precisely".
So unfortunately, I bought a battery that I didn't need, and I didn't keep the slightly-old one. It would be kinda'-handy to have a spare battery. I've been thinking about buying a portable "jump start box" and keeping it in the trunk, but I'd have to keep it charged and it's a rare problem anyway.