For original messy development history, see https://github.com/cgull/mosh/tree/localhost or https://github.com/cgull/mosh/commit/e7feed48a4a271e2977f714f58acfa04cdaa5cca
This tests cryptographic primitives implemented by others. It uses the same interfaces and indeed the same compiled object code as the Mosh client and server. It does not particularly test any code written for the Mosh project.
Keith Winstein