sub trim {
    for (@_) {
        s/^\s+//;
        s/\s+$//;
    }
}

##</code><code>##

subtest 'trim' => sub {
    is("leading", trim("   leading"), "trim: leading");
    ... more test cases ...
};

##</code><code>##

sub trim {
    for (@_) {
        next if is_readonly($_);
        s/^\s+//;
        s/\s+$//;
    }
}

##</code><code>##

subtest 'trim' => sub {
    my @test = ("  leading", "trailing  ", "  both  ");
    trim(my $tmp = "  leading");
    is("leading", $tmp, "trim: leading");
    trim($tmp = "trailing  ");
    is("trailing", $tmp, "trim: trailing");
    trim($tmp = "  both  ");
    is("both", $tmp, "trim: leading & trailing");
    trim(@test);
    my $out = "'".join("', '",@test)."'";
    is("'leading', 'trailing', 'both'", $out, "trim: list");
    done_testing();
};