Rather than take an exam, what if the users of the code comment on its efficacy? Let them answer questions like
a) In what application / context have you used this code?
b) Has it been useful to you as published or have you edited it before use ?
c) If any improvements are possible, will you suggest / contribute them?

If each comment is listed like those on sites like Baazee.com, the intending downloader will know forehand what to expect from the code.

Jerson