# Foo.pm package Foo; use strict; use warnings; use DateTime; sub new { my $class = shift; my $self = { _timevalue => DateTime->now, }; bless( $self, $class ); return $self; } # Modify _timevalue and return blessed reference sub _dumper_hook { $_[0] = bless { %{ $_[0] }, _timevalue => $_[0]->{_timevalue}->ymd . q{ } . $_[0]->{_timevalue}->hms, }, ref( $_[0] ); } 1; __END__ #### # Foo.t: use strict; use warnings; use Data::Dumper; use Test::More; plan tests => 2; use Foo; my $f = Foo::->new; { local $Data::Dumper::Freezer = '_dumper_hook'; like( Dumper($f), qr/\d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2}/, q{prints short version} ); } unlike( Dumper($f), qr/\d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2}/, q{prints long version} ); __END__ #### $ perl Foo.t 1..2 ok 1 - prints short version ok 2 - prints long version $