Allow modules to export custom fact values

[bodgit]

I'm using the service_provider fact from the stdlib module in my own modules. Because this fact won't be in facterdb I have to provide values for it. Now, I can do this using add_custom_fact :service_provider, ->(os, facts) { ... } however at least for this fact, the logic can be quite cumbersome. I also have to duplicate this logic across every module that uses this same fact.

It would be handy if (somehow) a module that provides a custom fact also exports some example values for use in tests split by OS which could then be picked up by rspec-puppet-facts. I'm not sure how it would work, but given every module dependency is available under spec/fixtures/modules/* during a test run some well-defined location in each module could be used. So stdlib would have example values that on for example, RHEL6, service_provider is init, on RHEL7 its systemd, plus all of the other OS values, etc.

I found voxpupuli/facterdb#49 which is about the package_provider fact, but it's the same problem.

[ekohl]

We have implemented this in https://github.com/voxpupuli/voxpupuli-test/blob/master/lib/voxpupuli/test/facts.rb