============== Foo.pm ==============
package Foo;

use strict;
require Exporter;

our @ISA = qw(Exporter);
our %EXPORT_TAGS = ( 'all' => [ qw(
   foo
) ] );

our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );

our $VERSION = '0.01';

sub foo
{
   die "This is being called from Foo\n";
}
1;
__END__
============== Bar.pm ==============
package Bar;

use strict;
use Foo qw(foo);
our $VERSION = '0.01';

sub new
{
   my ($class) = @_;
   my $self = [];
   bless($self, $class);
}

sub bar
{
   my ($self) = shift;
   foo();
}

1;
__END__
============== Baz.pl ==============
use strict;
use warnings;

use Test::MockModule;
use Bar;

{
   my $mock = Test::MockModule->new('Foo');
   $mock->mock('foo', sub {print "Successfully mocked!\n";});
   my $bar = Bar->new();
   $bar->bar();
}