package Test;

use strict;
use warnings;

sub new {
	my $this = shift;
	my $class = ref($this) || $this;
	my $self = {};
	bless($self, $class);

	$SIG{'__WARN__'} = sub { print 'WARNING: '.$_[0]; };

	return $self;
}

sub A {
	my $self = shift;

	warn 'This will trigger $SIG{__WARN__}';
}

sub B {
	my $self = shift;

	$self->NonExistingFunction();
}

my $test = Test->new();
$test->A();
$test->B();