Question

How do I unit-test my C code? Do I simply write a test.c for each module to test individual functions as well as the overall module?

Also, how do I test my whole C program under conditions such as low memory or bad input (someone trying to find a security exploit)?

Answer 1

in writing some functions in another module, that's a good idea, you can use your own Header (*.h). Trying to find a security exploit, i suggest to debug it (a traditional method but still being the powerful one i thought). Another way to find the security issues of your programs, you can Use Big O to define the worst case. For bad input, you should try in many conditions.
Happy Coding :)

Answer 2

Here are lot of unit testing tools and techniques for C http://stackoverflow.com/questions/65820/unit-testing-c-code