After fixing your typo:

    return "File does not exist\n";
        unless -e $_;
[download]

needs to become

    return "File does not exist\n"
        unless -e $_;
[download]

the program works for me:

C:\Projekte>perl -w tmp.pl
tmp.pl
readable writable
[download]

So, maybe tell us more exactly what you're typing in, what files exist, and maybe consider adding some more debugging output to your file.

Your form of calling the filetest function is bad/misleading. filetest is not using any parameters passed to it, it uses the global $_. So you should either call it as filetest(); or make your subroutine actually use its argument.

As a style note, I never use the ampersand notation for function calls (&filetest()) - I find it too dangerous, because when I leave off the parentheses (&filetest;), that has the unintended side effect of calling filetest with the current values of @_ instead of passing no parameters at all.