Add spec for CLocale module

spec/clocale_spec.rb

@@ -0,0 +1,15 @@
+require 'clocale'
+
+RSpec.describe CLocale do
+  context 'module' do
+    %i(LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME).each do |const|
+      it "has #{const} constant" do
+        expect(subject).to be_const_defined const
+      end
+    end
+
+    it 'setlocale' do
+      expect { subject.setlocale(CLocale::LC_ALL, '') }.not_to raise_error
+    end
+  end
+end