When importing an Ed25519 key pair in JWK format we need to ensure that the value in the 'x' and 'd' keys correspond valid key pair. We need to ensure that the public key generated from the value got from the 'd' key matches the value imported from the 'x' value. 

It's worth mentioning that the Web Cryptography API spec doesn't describes explicitly such test, but I think it's implied by the need of ensure the integrity of the import of key pairs in the JWK format. Additionally, there are Web Platform Tests that fail due t the lack of this check in WebKit's implementation of the Ed25519 algorithm.