In cryptography, subtle mistakes can have catastrophic consequences, and mistakes in open source cryptographic software libraries repeat too often and remain undiscovered for too long. Good implementation guidelines, however, are hard to come by: understanding how to implement cryptography securely requires digesting decades’ worth of academic literature. We recognize that software engineers fix and prevent bugs with unit testing, and we found that many cryptographic issues can be resolved by the same means. These observations have prompted us to develop Project Wycheproof, a collection of unit tests that detect known weaknesses or check for expected behaviors of some cryptographic algorithm. Our cryptographers have surveyed the literature and implemented most known attacks. As a result, Project Wycheproof provides tests for most cryptographic algorithms, including RSA, elliptic curve crypto, and authenticated encryption.