Spain’s health ministry says they’re “defective.” So does Turkey. Now Georgia has canceled its contract. Rapid COVID-19 tests made by Chinese company Bioeasy seemed like a great solution to the coronavirus testing shortage—and the gear was quickly bought up by one government after another. Then the complaints started rolling in, that one of the company’s products is wildly inaccurate.

So how big is the problem? How many more countries are dealing with Bioeasy’s busted COVID tests? And how do COVID-19 tests work?