Extracted method to return a function default into a utility method

lib/veritas/optimizer/algebra/summarization.rb

@@ -38,6 +38,19 @@ def optimize_summarize_per
         # Optimize when the operand is Empty
         class EmptyOperand < self
 
+          # Return the default value for a function
+          #
+          # @param [Object] function
+          #
+          # @return [Object]
+          #
+          # @api private
+          def self.extension_default(function)
+            if function.respond_to?(:default)
+              function.finalize(function.default)
+            end
+          end
+
           # Test if the operand is empty
           #
           # @return [Boolean]
@@ -60,15 +73,13 @@ def optimize
 
           # Return the extensions for the optimized relation
           #
-          # @return [Hhash{Attribute => #call}]
+          # @return [Hash{Attribute => #call}]
           #
           # @api private
           def extensions
             extensions = {}
             operation.summarizers.each do |attribute, function|
-              extensions[attribute] = if function.respond_to?(:default)
-                function.finalize(function.default)
-              end
+              extensions[attribute] = self.class.extension_default(function)
             end
             extensions
           end

spec/unit/veritas/optimizer/algebra/summarization/empty_operand/class_methods/extension_default_spec.rb

@@ -0,0 +1,22 @@
+# encoding: utf-8
+
+require 'spec_helper'
+
+describe Optimizer::Algebra::Summarization::EmptyOperand, '.extension_default' do
+  subject { object.extension_default(function) }
+
+  let(:object) { described_class }
+
+  context 'when the function has a default' do
+    let(:operand)  { mock('Operand')               }
+    let(:function) { Aggregate::Count.new(operand) }
+
+    it { should eql(0) }
+  end
+
+  context 'when the function does not have a default' do
+    let(:function) { proc {} }
+
+    it { should be_nil }
+  end
+end

veritas-optimizer.gemspec

@@ -174,6 +174,7 @@ Gem::Specification.new do |s|
     "spec/unit/veritas/optimizer/algebra/restriction/tautology/optimize_spec.rb",
     "spec/unit/veritas/optimizer/algebra/restriction/unoptimized_operand/optimizable_spec.rb",
     "spec/unit/veritas/optimizer/algebra/restriction/unoptimized_operand/optimize_spec.rb",
+    "spec/unit/veritas/optimizer/algebra/summarization/empty_operand/class_methods/extension_default_spec.rb",
     "spec/unit/veritas/optimizer/algebra/summarization/empty_operand/optimizable_spec.rb",
     "spec/unit/veritas/optimizer/algebra/summarization/empty_operand/optimize_spec.rb",
     "spec/unit/veritas/optimizer/algebra/summarization/empty_summarize_per/optimizable_spec.rb",