test.pl

{

    package Bar;
    use strict;
    use warnings;

    use base qw(Class::Accessor::Fast);

    sub register_hook {
        my ($self, $context) = @_;

        $context->add_trigger(
            name     => 'hook',
            callback => $self->can('bar'),
        );
    }

    sub bar {
        my ($self, $bar) = @_;

        warn $self;
        warn $bar;
    }
}

{

    package Foo;
    use strict;
    use warnings;

    use base qw(Class::Accessor::Fast);
    use Class::Trigger;

    sub new {
        my $class = shift;

        my $self = bless {}, $class;
        my $plugin = Bar->new;
        $plugin->register_hook($self);
        return $self;
    }

    sub run {
        my $self = shift;

        $self->call_trigger('hook',  'BAR');
    }
}

my $foo = Foo->new;
$foo->run;