Ensure regions cannot be modified outside gem

lib/carmen/region.rb

@@ -21,7 +21,7 @@ def name
     end
 
     def subregions
-      @subregions ||= load_subregions
+      @subregions ||= load_subregions.freeze
     end
 
     def subregions?

spec/carmen/country_spec.rb

@@ -2,9 +2,20 @@
 
 describe Carmen::Country do
 
-  it "provides access to all countries" do
-    countries = Carmen::Country.all
-    countries.size.must_equal 3
+  describe "all" do
+    before do
+      @countries = countries = Carmen::Country.all
+    end
+
+    it "provides access to all countries" do
+      @countries.size.must_equal 3
+    end
+
+    it "denies modification of countries" do
+      assert_raises RuntimeError do
+        @countries.clear
+      end
+    end
   end
 
   describe "API for finding countries by name" do

spec/carmen/region_spec.rb

@@ -30,6 +30,16 @@
     end
 
     describe "subregions" do
+      it "is frozen" do
+        subregions = Carmen::Country.coded('OC').subregions
+
+        assert_raises RuntimeError do
+          subregions.clear
+        end
+      end
+    end
+
+    describe "subregion" do
       before do
         @london = @airstrip_one.subregions.first
       end