Updated 2020-04-16: It’s planned to add an extra round blake2b on eaglesong output in Testnet.
PoW testnets are prone to the denial-of-service attack. Although there’s an proposal to use PoA in Aggron, it requires significant changes to the codebase and has been hold.
Since there’s little economic incentive to mine on testnets using dedicated hardware resources, it is reasonable to assume that most of the DoS attacks are caused by mining tests and miners accidentally connected to the testnet. Based on this assumption, this proposal suggests to use a variant of the PoW algorithm in Aggron to relieve the attack problem.