common libs go into the lib/common directory

spec/lib/common/updater/updater_spec.rb

@@ -0,0 +1,27 @@
+# encoding: UTF-8
+
+require 'spec_helper'
+
+describe Updater do
+
+  before :all do
+    class TestUpdater < Updater
+    end
+  end
+
+  after :all do
+    Object.send(:remove_const, :TestUpdater)
+  end
+
+  describe 'non implementation of #is_installed?, #has_update? and #update' do
+    it 'should raise errors' do
+      test_updater = TestUpdater.new
+      methods_to_call = [:is_installed?, :update, :local_revision_number]
+
+      methods_to_call.each do |method_to_call|
+        expect { test_updater.send(method_to_call) }.to raise_error(NotImplementedError)
+      end
+    end
+  end
+
+end