CODEWITHSUNDEEP
cunit-testingmockingstub
jungon
jungon

Reputation: 39

Ways to mock C functions for unit-testing?

I've tried multiple sources for solutions to this problem. They all either require modifying the source code, and architecture specific exploit such as writing in a jmp instruction to detour the function, or using a macro and including the c file. The first one is extremely annoying to deal with, the second is usually not possible due to page protections, and the third introduces a lot of problems with linking multiple files containing different mocks and unit test for the same source file. Is there any better method of doing this?

Upvotes: 0

Views: 884

Answers (1)

davidriod
davidriod

Reputation: 1057

You can user function pointer in your nominal code. You assign them at init with nominal implemetation in your application. In your unit test you can then assign the function pointer to the mock implmentation. Function pointer is a common practice used to implement interface in C.

Here is a gist of how that could be done:

typedef struct {
    void (*method) ();
} interface;

void run(itf *interface)
{
    itf->method();
}

void methodImpl()
{
    printf("nominal code");
}

void methodMock()
{
    printf("mock code");
}

void do_run()
{
   interface itf;

   itf.method = methodImpl;
   run(&itf);
}

void test_run()
{
   interface itf;

   itf.method = methodMock;
   run(&itf);
}

Upvotes: 2

Related Questions