Binary nodes should not generate the same hash as nodes of other classes

lib/arel/nodes/binary.rb

@@ -16,7 +16,7 @@ module Arel
       end
 
       def hash
-        [@left, @right].hash
+        [self.class, @left, @right].hash
       end
 
       def eql? other

test/nodes/test_binary.rb

@@ -0,0 +1,26 @@
+require 'helper'
+require 'set'
+
+module Arel
+  module Nodes
+    describe 'Binary' do
+      describe '#hash' do
+        it 'generates a hash based on its value' do
+          eq = Equality.new('foo', 'bar')
+          eq2 = Equality.new('foo', 'bar')
+          eq3 = Equality.new('bar', 'baz')
+
+          assert_equal eq.hash, eq2.hash
+          refute_equal eq.hash, eq3.hash
+        end
+
+        it 'generates a hash specific to its class' do
+          eq = Equality.new('foo', 'bar')
+          neq = NotEqual.new('foo', 'bar')
+
+          refute_equal eq.hash, neq.hash
+        end
+      end
+    end
+  end
+end