I've never liked having to type my test twice, once for the actual test and once for the 'message'. So I do something more like this instead:

  #include <stdio.h>
  #define test(expr) do {                              \
          if (!(expr)) printf("FAILED: %s\n", #expr);  \
          else printf("    ok: %s\n", #expr);          \
      } while (0)
  
  int main(void) {
      int a = 1;
      test(a == 1);
      test(a == 0);
      return 0;
  }

I don't actually use the direct printf() approach, but this shows the idea. Is there a reason more people don't 'stringify' macro arguments? I'm pretty tied to GCC, and am not always aware of what works on other compilers.