#!/usr/bin/perl
  
  use Your::Module;
  use Proc::Background;
  use Test::Resub qw(resub);

  # disable Proc::Background->new for the scope of this block
  {
    my $fake_new = sub {
      return bless {}, 'Proc::Background'; # or whatever
    };
    my $resub = resub 'Proc::Background::new', $fake_new;

    # continue on your merry way, content knowing that
    # your $fake_new is getting called.
  }
  # scope of $resub object ends, its DESTROYER restores
  # the original Proc::Background::new.