add a factory method for production LOWER functions

lib/arel/factory_methods.rb

@@ -25,5 +25,11 @@ module Arel
     def grouping expr
       Nodes::Grouping.new expr
     end
+
+    ###
+    # Create a LOWER() function
+    def lower column
+      Nodes::NamedFunction.new 'LOWER', [column]
+    end
   end
 end

test/test_factory_methods.rb

@@ -22,6 +22,13 @@ module Arel
         assert_instance_of Nodes::On, on
         assert_equal :one, on.expr
       end
+
+      def test_lower
+        lower = @factory.lower :one
+        assert_instance_of Nodes::NamedFunction, lower
+        assert_equal 'LOWER', lower.name
+        assert_equal [:one], lower.expressions
+      end
     end
   end
 end