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