Add SPEC_FACTS_STRICT setting

Folks with high confidence needs can use this to elide the permissive
behaviour.

README.md

@@ -364,3 +364,5 @@ If you want to run the tests against the facts for specific operating systems, y
 ```bash
 SPEC_FACTS_OS='ubuntu-14' rake spec
 ```
+
+When no facts are available for the specific facter/operating system combination, the library will fall back to facts from earlier versions of the requested operating system, to allow testing to continue when new versions of facter are released. Set `SPEC_FACTS_STRICT=yes` to instead trigger a failure.

lib/rspec-puppet-facts.rb

@@ -88,6 +88,14 @@ def on_supported_os(opts = {})
       return {}
     end
 
+    unless version == facterversion
+      if RspecPuppetFacts.spec_facts_strict?
+        raise ArgumentError, "No facts were found in the FacterDB for Facter v#{facterversion}, aborting"
+      else
+        RspecPuppetFacts.warning "No facts were found in the FacterDB for Facter v#{facterversion}, using v#{version} instead"
+      end
+    end
+
     os_facts_hash = {}
     received_facts.map do |facts|
       # Fix facter bug
@@ -170,6 +178,13 @@ def self.spec_facts_os_filter
     ENV['SPEC_FACTS_OS']
   end
 
+  # If SPEC_FACTS_STRICT is set to `yes`, RspecPuppetFacts will error on missing FacterDB entries, instead of warning & skipping the tests, or using an older facter version.
+  # @return [Boolean]
+  # @api private
+  def self.spec_facts_strict?
+    ENV['SPEC_FACTS_STRICT'] == 'yes'
+  end
+
   # These facts are common for all OS'es and will be
   # added to the facts retrieved from the FacterDB
   # @api private

spec/rspec_puppet_facts_spec.rb

@@ -397,18 +397,27 @@
           supported_os: [
             { 'operatingsystem' => 'CentOS', 'operatingsystemrelease' => %w[7] }
           ],
-          facterversion: "#{major}.#{minor.to_i + 1}"
+          facterversion: "#{major}.#{minor.to_i + 100}"
         )
       end
 
       it 'returns facts from a facter version matching future and below' do
         major, minor = Facter.version.split('.')
         is_expected.to match(
           'centos-7-x86_64' => include(
-            facterversion: /\A#{major}\.[0-#{minor.to_i + 1}]\./
+            facterversion: /\A#{major}\.[0-#{minor.to_i + 100}]\./
           )
         )
       end
+
+      context 'With SPEC_FACTS_STRICT set to `yes`' do
+        before(:each) do
+          allow(RspecPuppetFacts).to receive(:spec_facts_strict?).and_return(true)
+        end
+        it 'errors' do
+          expect { subject }.to raise_error ArgumentError, /No facts were found in the FacterDB.*aborting/
+        end
+      end
     end
 
     context 'With a custom facterversion (3.1) in the options hash' do