static char* valid_keys[] = {
        "callbacks", "can", "default", "depends", "isa", "optional", "regex", "type"
    };
    HE* he;
    hv_iterinit(spec);
    while (he = hv_iternext(spec)) {
        STRLEN len;
        char* key = HePV(he, len);
        int ok = 0;
        int j;
        for (j=0; j < sizeof(valid_keys)/sizeof(valid_keys[0]); j++) {
            if (strcmp(key, valid_keys[j]) == 0) {
                ok = 1;
                break;
            }
        }
        if (!ok) {
            SV* buffer = sv_2mortal(newSVpv("'",0));
            sv_catpv(buffer, key);
            sv_catpv(buffer, "': unknown option error\n");
            FAIL(buffer, options);
        }
    }

##</code><code>##

$ ./841578.pl
1..4
'callback': unknown option error
 at ./841578.pl line 14
        main::howareyoufeelingtoday('happy') called at ./841578.pl line 18
# Looks like your test exited with 9 before it could output anything.