[jlgreco]

With normal software you can load up on the unit and integration tests to make yourself more confident with your software. When the concern is with the integrity of a cryptographic system, things are not quite so simple. You can write tests, sure, but your overall confidence afterwards is going to be much different.

[IsThisObvious]

We go beyond unit tests to verify that the algorithms can't create certain states by any execution path, etc.

Formal verification of software properties is an interesting field.

[DanBC]

A blog post about the process would be fascinating, and probably something that many on HN would be interested in.