sub argumentTest {
    my ($booleanArg) = @_;

    if (!defined($booleanArg)) {
        return "null";
    }
    elsif ($booleanArg eq "false") {
        return "false";
    }
    elsif ($booleanArg eq "true") {
        return "true";
    }
    else {
        return "unknown";
    }

   return "Unreachable code: cannot be covered";
}