Matcher for be a subset

README.md

@@ -31,6 +31,12 @@ Even better, you can run all of these tests for every file in a directory like s
 
 ## Testing the validity of your translation data
 
+To test that your locale file is a subset of the default locale file
+
+	describe "config/locales/fr.yml" do
+	  it { should be_a_subset_of 'config/locales/en.yml' }
+	end
+
 If you need to test that all translations have been completed :
 
     describe "config/locales/fr.yml" do

lib/i18n-spec/matchers/be_a_subset_of_matcher.rb

@@ -0,0 +1,14 @@
+RSpec::Matchers.define :be_a_subset_of do |expected|
+  match do |actual|
+    @locale_file = I18nSpec::LocaleFile.new(actual)
+    @default_locale = I18nSpec::LocaleFile.new(expected)
+    @superset = @locale_file.flattened_translations.keys.reject do |key|
+      @default_locale.flattened_translations.keys.include?(key)
+    end
+    @superset.empty?
+  end
+
+  failure_message_for_should do |player|
+    "expected #{@locale_file.filepath} to not include :\n- " << @superset.join("\n- ")#{@superset.join"
+  end
+end

lib/i18n-spec/models/locale_file.rb

@@ -2,10 +2,20 @@ module I18nSpec
   class LocaleFile
     PLURALIZATION_KEYS = %w{zero one two few many other}
 
+    attr_accessor :filepath
+
     def initialize(filepath)
       @filepath = filepath
     end
 
+    def translations
+      @translations ||= Psych.load_file(@filepath)
+    end
+
+    def flattened_translations
+      @flattened_translations ||= flatten_tree(translations.values.first)
+    end
+
     def is_parseable?
       begin
         Psych.load_file(@filepath)
@@ -39,10 +49,6 @@ def is_a_complete_tranlsation_of?(default_locale_filepath)
 
   protected
 
-    def translations
-      @translations ||= Psych.load_file(@filepath)
-    end
-
     def flatten_tree(data, prefix = '', result = {})
       data.each do |key, value|
         current_prefix = prefix.empty? ? key.to_s : "#{prefix}.#{key}"

spec/fixtures/not_subset.yml

@@ -0,0 +1,9 @@
+en:
+  dogs:
+    zero: 'no dogs'
+    one: 'one dog'
+    other: '%{count} dogs'
+  itteh:
+    bitteh:
+      ceiling:
+        doggeh: 'is asking for trouble'

spec/lib/i18n-spec/matchers_spec.rb

@@ -9,14 +9,17 @@
   it { 'spec/fixtures/invalid_pluralization_keys.yml'.should_not have_valid_pluralization_keys }
   it { 'spec/fixtures/multiple_top_levels.yml'.should_not have_one_top_level_namespace }
   it { 'spec/fixtures/multiple_top_levels.yml'.should_not be_named_like_top_level_namespace }
+  it { 'spec/fixtures/not_subset.yml'.should_not be_a_subset_of 'spec/fixtures/en.yml' }
 end
 
 describe "Translated files" do
   describe 'spec/fixtures/fr.yml' do
+    it { should be_a_subset_of 'spec/fixtures/en.yml' }
     it { should be_a_complete_translation_of 'spec/fixtures/en.yml' }
   end
 
   describe 'spec/fixtures/es.yml' do
+    it { should be_a_subset_of 'spec/fixtures/en.yml' }
     it { should_not be_a_complete_translation_of 'spec/fixtures/en.yml'}
   end
 end