The fridge test is where you put the oil in the fridge. If it becomes solid or has lots of solid blobs after a day or two, then it's olive oil. However, you can still get solids even if it's been diluted with crap oils so it's not fool-proof.
The other test is the lamp oil test. Real olive oil can keep an oil lamp burning. This, too, is only partially reliable.
Fortunately there are olive farms near me so I can get olive oil from local farmers. It's just going to cost me way more than $6 for a quart like at Trader Joe's. I've never priced it. I figured since I had to ask, I probably couldn't afford it. I wouldn't be surprised if it costs $20 or even $40 a quart.
Female, 5'3", 48, Starting weight: 163lbs. Current weight: 135.
Starting bench press: 30lbs. Current bench press: 75lbs.