unit.h

#ifndef _UNIT_H_
#define _UNIT_H_

#define mu_assert(message, test) do { if (!(test)) return message; } while (0)
#define mu_run_test(test) do { char *message = test(); tests_run++;     \
        if (message) {failed++; return message;} } while (0)
extern int tests_run;
extern int failed;

#endif

usage.c

#include "unit.h"

int tests_run = 0;
int failed = 0;

static char *the_test() {
   int subject = 0;
   mu_assert("test subject failed", subject == 0);
   return NULL;
}

int main(int argc, char **argv) {
   char *res = mu_run_test(the_test);
    if (result) {
        printf("\n%s\n", result);
    }
    else {
        printf("\t\t\t\t...ALL TESTS PASSED\n");
    }
    printf("Tests run: %d, failed tests %d\n",
           tests_run, failed);
}