Along with my resume, i am posting a program which is a solution to a coding challenge on the company's website. What should accompany the code so that it really impresses the reviewer?
Anything else i should add, or is it already overkill?
Thanks.
But you repeat yourself....
Aside from that, 'showing your working-out', like in a math-test is good.
Explain your reasoning behind the design of the application, bugs you encountered and how you found/fixed them, some challenges you faced and how you dealt with them. If you show how you can solve the little problems with the big picture still in mind, that shows good perspective that is valuable for a developer job.
Tests are definitively a must, the quality and coverage of the unit tests is usually equivalent to the quality of the overall code.
Beware of comments of any kind, as stated in Clean Code, and many other books, comments are most of the time just an excuse for poor written code.
Try to keep your code as expressive as possible without the need for comments, and with the test coverage near 90 - 100 %. That should give a very good impression IMHO.