As a general rule I'm always in favor for the shortest meaningful name.

In this particular case since it's just for testing, and in the mockup/manufacture I'm inclined to these variations (in the order of preference):
 * `md5()`
 * `makeMD5()` -- it follows in the same path as `makeNumber()`, 'makeString()` but it forces us to capitalize the `MD5` part.
 * `md5Digest()`

Any of these should be fine. Thanks!