A pretty expensive (Samsung) USB-drive I have causes weird errors. The problem might be a computer I have connected it to (this computer's SSD broke down in a similar way) but to rule out that it is this USB stick that is broken I would like to perform a hardware test on it. How can I do that on a Mac?
Open the Terminal.app in Applications/Utilities.
Cut and paste this inside to install Brew:
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Install e2fsprogs with brew:
brew install e2fsprogs
diskutil list to find your device (/dev/diskX)
badblocks on your device: (replace the X with your device number)
/usr/local/Cellar/e2fsprogs/1.44.3/sbin/badblocks -v /dev/diskX