About Testing products for dropshipping (beginner)

I have a limited budget of around $500-$700, and I understand how important it is to test products when dropshipping. How much money should I spend on one product (in terms of ads) until I kill it and move on?

Also, do I have to make a new store every time to test products? Do I actually sell? Or do I just run ads and look at the results?

Anything else I should know about testing products? Thanks!