@mixin test($arglist...) {
    $map: keywords($arglist);
    answer: if($map, "Yep", "Nope");
}

with-keyword-args{
    @include test($arg1: one, $arg2: two, $arg3: three);
}
with-no-args {
    @include test();
}
without-keyword-args {
    @include test(not-a-keyword-arg-1 , not-a-keyword-arg-2);
}