# App.pm
package App;

use Foo;

sub new {
    my $class = shift;
    bless { ua => Foo->new }, $class;
}

sub check {
    my $self = shift;
    my $res = $self->{ua}->get('https://perlmonks.org');
    if ($res->code != 200) {
        return "Monks are offline";
    }
    return "Everything works just fine";
}

1;

##</code><code>##

# Foo.pm
package Foo;
use parent 'LWP::UserAgent';
1;

##</code><code>##

# test_v1.pm

package Foo;
use HTTP::Response;

sub get { return HTTP::Response->new(500); }

# Add more packages ad libidum
1;

##</code><code>##

# errorcode.t

use test_v1;
# %INC modification, as prescribed by LanX
#BEGIN {
#    $INC{'Foo.pm'} = __FILE__;
#}

use Test::More;
use App;

my $app = App->new;
is($app->check,"Monks are offline");

done_testing;