When I want to test a new flash drive to make sure the entire drive is good regarding reading and writing, I usually use "H2testw" and "USB Flash Drive Tester". (I'll run H2testw first, which overwrites data but doesn't destroy formatting. Then I'll run USB Flash Drive Tester, which overwrites data *and* destroys formatting. After that, I'll have to reformat the flash drive. I'm a fan of using Rufus for most of my flash drive formatting.)
This link mentions 11 programs. I've only used less than half of them, so I can't vouch for most of them. I only included this link as something for further research: https://www.geckoandfly.com/22803/detect-fake-usb-flash-drives-sd-cards-ssd-disk/
Warning! - These programs often overwrite data and may even destroy the formatting of the flash drive. So back up any important files from the drive before testing! (ValiDrive should be safe for your data, but I'd back up any important data even when using ValiDrive.)
I don't think I have any fake flash drives, but they're showing up more often on Amazon. (Did you buy one of those no-name 1 terabyte flash drives for 15 or 20 dollars?)
Steve Gibson has just finished his nifty little freeware utility that should be able to tell you if that flash drive is legit or fake. (There are a few other freeware programs that also promise to do that, but Steve had to put his own twist on the issue. It never hurts to have another option to solve a problem!)
ValiDrive is for Windows only (Win 7 and newer). If you're running Linux or Mac, there are reports that ValiDrive runs well in a virtual machine. I'm not sure if it also runs in WINE; Maybe the ValiDrive FAQ page will answer that question soon.
Note that ValiDrive only checks for the fake/legit issue. It does *NOT* test *all* of the drive's blocks for readability and writeability. (It spot-checks 576 locations on the drive, but not the entire drive.)
Steve's site has some information pages that explain the program in more detail. However, he's still working on the FAQ page, so you might want to revisit the FAQ page in a few days.
https://www.grc.com/validrive.htm