Updater cleanup

lib/updater/updater.rb

@@ -27,21 +27,15 @@ class Updater
   end
 
   def is_installed?
-    raise_must_be_implemented()
+    raise NotImplementedError
   end
 
   def local_revision_number
-    raise_must_be_implemented()
+    raise NotImplementedError
   end
 
   def update
-    raise_must_be_implemented()
-  end
-
-  protected
-
-  def raise_must_be_implemented
-    raise "The method must be implemented"
+    raise NotImplementedError
   end
 
 end

spec/lib/updater/updater_spec.rb

@@ -17,7 +17,7 @@ describe Updater do
       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
+        expect { test_updater.send(method_to_call) }.to raise_error(NotImplementedError)
       end
     end
   end