adding node test

test/nodes/test_node.rb

@@ -0,0 +1,33 @@
+require 'helper'
+
+module Arel
+  class TestNode < MiniTest::Unit::TestCase
+    def test_all_nodes_are_nodes
+      Nodes.constants.map { |k|
+        Nodes.const_get(k)
+      }.grep(Class).each do |klass|
+        next if Nodes::SqlLiteral == klass
+        assert klass.ancestors.include?(Nodes::Node), klass.name
+      end
+    end
+
+    def test_each
+      list = []
+      node = Nodes::Node.new
+      node.each { |n| list << n }
+      assert_equal [node], list
+    end
+
+    def test_generator
+      list = []
+      node = Nodes::Node.new
+      node.each.each { |n| list << n }
+      assert_equal [node], list
+    end
+
+    def test_enumerable
+      node = Nodes::Node.new
+      assert_kind_of Enumerable, node
+    end
+  end
+end