package Logger;
use warnings;
use strict;

use Exporter qw{ import };
our @EXPORT = qw{ log_warn };

sub log_warn { warn @_ }

__PACKAGE__

##</code><code>##

package Common;
use warnings;
use strict;
use experimental qw( signatures );

use Logger;
use Moose::Exporter;

my ($import, $unimport, $init_meta) = Moose::Exporter->build_import_methods(
    as_is => [\&Logger::log_warn]
);
sub import { goto &$import }

__PACKAGE__

##</code><code>##

package MyObj;

use Moose;
use Common;
use namespace::autoclean;
use experimental qw{ signatures };

has value => (is => 'ro', required => 1);

sub foo($self) {
    log_warn('Value too large') if $self->value > 10;
}

__PACKAGE__->meta->make_immutable

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;

use Test::More tests => 2 * 2;

use Sub::Override;

my @warnings;
my $override;

use MyObj;
BEGIN {
    $override = 'Sub::Override'->new(
        'MyObj::log_warn' => sub { push @warnings, $_[0] });
}

for my $test ([1, undef, 'no warnings'], [11, 'Value too large', 'warnings']) {
    my ($value, $warnings, $name) = @$test;
    @warnings = ();
    my $o = bless {value => $value}, 'MyObj';
    ok($o, 'constructs');
    $o->foo;
    is($warnings[0], $warnings, $name);
}

##</code><code>##

t/01-basic.t .. 
1..4
Cannot replace non-existent sub (MyObj::log_warn) at t/01-basic.t line 15.
BEGIN failed--compilation aborted at t/01-basic.t line 16.
# Looks like your test exited with 255 before it could output anything.
Dubious, test returned 255 (wstat 65280, 0xff00)
Failed 4/4 subtests 

Test Summary Report
-------------------
t/01-basic.t (Wstat: 65280 Tests: 0 Failed: 0)
  Non-zero exit status: 255
  Parse errors: Bad plan.  You planned 4 tests but ran 0.

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;

use Test::More tests => 2 * 2;

use Sub::Override;

my @warnings;
my $override;

use Logger;
BEGIN {
    $override = 'Sub::Override'->new(
        'Logger::log_warn' => sub { 'WHATEVER' });
}
use MyObj;
BEGIN {
    *MyObj::log_warn = sub { push @warnings, $_[0] };
}

for my $test ([1, undef, 'no warnings'], [11, 'Value too large', 'warnings']) {
    my ($value, $warnings, $name) = @$test;
    @warnings = ();
    my $o = bless {value => $value}, 'MyObj';
    ok($o, 'constructs');
    $o->foo;
    is($warnings[0], $warnings, $name);
}