ok( ! ($mode & 022), "File is not group or world writable" );
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I've just seen a presentation on Coccinelle, this kind of error was quite common in the Linux kernel. See here.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

Here's one non-scientific way to check:

#!/usr/bin/perl

use warnings;
use strict;

use Test::More;

my $file = 'file.txt';

my $perms = sprintf("%o", (stat $file)[2] & 0777); 

my ($u, $g, $w) = split //, $perms;

my @writable = qw(2 3 6 7);

ok (!(grep /$g/, @writable), "File is not group writable");

ok (!(grep /$w/, @writable), "File is not world writable");
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-stevieb

G'day Neil,

I see answers identifying a precedence problem. Rather than using the ! operator and adding (multiple levels of) parentheses, you can just use the low-precedence equivalent: not (see "perlop: Operator Precedence and Associativity"). There's also low-precedence and, or and xor. I find these operators make the code easier to read than using parentheses: you, of course, may have a different preference.

Instead of using Test::More's ok() function (and, where necessary, negating the test), consider using the is() and isnt() functions. This (at least in the case of your posted code) circumvents the precedence issue entirely; it also aligns the test function with the test description. Here's an example roughly based on your code:

#!/usr/bin/env perl

use strict;
use warnings;

use Test::More tests => 4;

my $mode = (stat $0)[2];

isnt(-d $0,       1,   "This script isn't a directory.");
is(  -O $0,       1,   "This script is owned by real uid.");
isnt($mode & 020, 020, "This script isn't group writable.");
isnt($mode & 002, 002, "This script isn't world writable.");
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[Note that I've used the core (builtin) stat function. File::stat, by default, overrides this.]

Output:

1..4
ok 1 - This script isn't a directory.
ok 2 - This script is owned by real uid.
ok 3 - This script isn't group writable.
ok 4 - This script isn't world writable.
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Update: While my intent was to compare ok() with is() and isnt(), which I believed I achieved, I did notice a bug in the example code. I've fixed the code; retested; and posted the new code and output. The offending line was:

isnt((stat $0)[2] & 022, 022, "This script isn't group or world writab
+le.");
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Update 2: My bug fix (from the initial update) left the code a bit messy. I've tidied that up. Now just one call to stat with the result stored in $mode. Retested successfully; output unchanged; new code posted.

I see, another way to the answer is via Basic debugging checklist

$ perl -MO=Deparse,-p

ok( ! $mode & 022, "File is not group or world writable" );
^Z
ok(((!$mode) & 18), 'File is not group or world writable');
- syntax OK
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