feat(_mapdata_spec): dump YAML back to string for better diffs

Provide a full breakdown of the method used to prepare the comparison
between both files.

ssf/files/default/inspec/controls/_mapdata_spec.rb

@@ -5,19 +5,43 @@
 control '`map.jinja` YAML dump' do
   title 'should match the comparison file'
 
-  # Strip the `platform[:finger]` version number down to the "OS major release"
-  mapdata_file = "_mapdata/#{system.platform[:finger].split('.').first}.yaml"
+  ### Method
+  # The steps below for each file appear convoluted but they are both required
+  # and similar in nature:
+  # 1. The earliest method was to simply compare the files textually but this often
+  #    led to false positives due to inconsistencies (e.g. spacing, ordering)
+  # 2. The next method was to load the files back into YAML structures and then
+  #    compare but InSpec provided block diffs this way, unusable by end users
+  # 3. The final step was to dump the YAML structures back into a string to use
+  #    for the comparison; this both worked and provided human-friendly diffs
 
-  # Load the mapdata from profile https://docs.chef.io/inspec/profiles/#profile-files
-  mapdata_dump = YAML.safe_load(inspec.profile.file(mapdata_file))
+  ### Comparison file for the specific platform
+  ### Static, adjusted as part of code contributions, as map data is changed
+  # Strip the `platform[:finger]` version number down to the "OS major release"
+  platform_finger = system.platform[:finger].split('.').first.to_s
+  # Use that to set the path to the file (relative to the InSpec suite directory)
+  mapdata_file_path = "_mapdata/#{platform_finger}.yaml"
+  # Load the mapdata from profile, into a YAML structure
+  # https://docs.chef.io/inspec/profiles/#profile-files
+  mapdata_file_yaml = YAML.safe_load(inspec.profile.file(mapdata_file_path))
+  # Dump the YAML back into a string for comparison
+  mapdata_file_dump = YAML.dump(mapdata_file_yaml)
 
-  # Derive the location of the dumped mapdata
+  ### Output file produced by running the `_mapdata` state
+  ### Dynamic, generated during Kitchen's `converge` phase
+  # Derive the location of the dumped mapdata (differs for Windows)
   output_dir = platform[:family] == 'windows' ? '/temp' : '/tmp'
-  output_file = "#{output_dir}/salt_mapdata_dump.yaml"
+  # Use that to set the path to the file (absolute path, i.e. within the container)
+  output_file_path = "#{output_dir}/salt_mapdata_dump.yaml"
+  # Load the output into a YAML structure using InSpec's `yaml` resource
+  # https://github.com/inspec/inspec/blob/49b7d10/lib/inspec/resources/yaml.rb#L29
+  output_file_yaml = yaml(output_file_path).params
+  # Dump the YAML back into a string for comparison
+  output_file_dump = YAML.dump(output_file_yaml)
 
   describe 'File content' do
     it 'should match profile map data exactly' do
-      expect(yaml(output_file).params).to eq(mapdata_dump)
+      expect(output_file_dump).to eq(mapdata_file_dump)
     end
   end
 end