InfixOperations are valid value expressions per SQL99 BNF, and

should support ordering

lib/arel/nodes/infix_operation.rb

@@ -4,6 +4,7 @@ module Nodes
     class InfixOperation < Binary
       include Arel::Expressions
       include Arel::Predications
+      include Arel::OrderPredications
       include Arel::AliasPredication
       include Arel::Math
 

test/nodes/test_infix_operation.rb

+require 'helper'
+
+module Arel
+  module Nodes
+    class TestInfixOperation < MiniTest::Unit::TestCase
+      def test_construct
+        operation = InfixOperation.new :+, 1, 2
+        assert_equal :+, operation.operator
+        assert_equal 1, operation.left
+        assert_equal 2, operation.right
+      end
+
+      def test_operation_alias
+        operation = InfixOperation.new :+, 1, 2
+        aliaz = operation.as('zomg')
+        assert_kind_of As, aliaz
+        assert_equal operation, aliaz.left
+        assert_equal 'zomg', aliaz.right
+      end
+
+      def test_opertaion_ordering
+        operation = InfixOperation.new :+, 1, 2
+        ordering = operation.desc
+        assert_kind_of Ordering, ordering
+        assert_equal operation, ordering.expr
+        assert_equal :desc, ordering.direction
+      end
+    end
+  end
+end