How can I override facter's os facts during local testing on a different operating system? – Debian

Environment

I am currently using Puppet 6.21.1 on Ruby 2.7.4 with PDK 2.3.0 (mostly for linting and launching the Puppet console as a REPL). The OS is macOS Monetery. If it matters, I’m running Ruby under RVM 1.29.12-next with a module-specific gemset.

Objective

I’m trying to test some Hiera lookups within a module on a macOS machine, and am trying to override the kernel, os, and osfamily facts returned on the development box by facter.

[See notes on the X/Y problem at the bottom of the post.]

What I’ve Tried

I have tried using the FACTERLIB environment variable, various individually-set FACTER_ environment variables, and a custom facts directory with the facter --custom-dir flag. While I have limited success my setting top-level variables with individual FACTER_ prefixed environment variables, I can’t seem to get facter to return a defined Hash for facter os that I copied from a Debian or Ubuntu host, which is what I’m currently trying to do for reasons I touch on below.

My current fact override looks like this:

# ${module_repository?}/.myfacts/os.rb

Facter.add(:os) do
  confine :kernal => 'Darwin'
  has_weight = 1_000

  setcode do
    {
      architecture => 'amd64',
      distro => {
        codename => 'focal',
        description => 'Ubuntu 20.04.3 LTS',
        id => 'Ubuntu',
        release => {
          full => '20.04',
          major => '20.04',
        },
      },
      family => 'Debian',
      hardware => 'x86_64',
      name => 'Ubuntu',
      release => {
        full => '20.04',
        major => '20.04',
      },
      selinux => {
        enabled => false,
      },
    }
  end
end

Unfortunately, calling facter --custom-dir=".myfacts" facter os from within the module’s top-level directory results in the standard facts (give or take the top-level facter element, which doesn’t appear in the output when not running overrides) for macOS Monterey:

facter => 
os => {
  architecture => "x86_64",
  family => "Darwin",
  hardware => "x86_64",
  macosx => {
    build => "21A559",
    product => "macOS",
    version => {
      full => "12.0.1",
      major => "12",
      minor => "0",
      patch => "1"
    }
  },
  name => "Darwin",
  release => {
    full => "21.1.0",
    major => "21",
    minor => "1"
  }
}

Both the X and the Y in my X/Y Problem

How can I get facter to report itself as a Debian-family Ubuntu system so that I can properly test my Hiera v5 lookups under ${module_respository?}/data/os/Debian.yaml from PDK console on my non-Puppetized Darwin development system?