Use the fake library
examples/fake-module/t/use_fake.t
use strict; use warnings; use Test::More; plan tests => 1; use Cwd qw(abs_path); use File::Basename qw(dirname); use lib dirname(abs_path($0)) . '/lib'; use WWW::Mechanize; diag $WWW::Mechanize::VERSION; is $WWW::Mechanize::VERSION, 'fake';