An error is now raised if you try to define the same attribute twice

lib/factory_girl/factory.rb

@@ -91,6 +91,11 @@ class Factory
   #     If no block is given, this value will be used for this attribute.
   def add_attribute (name, value = nil, &block)
     attribute = Attribute.new(name, value, block)
+
+    if attribute_defined?(attribute.name)
+      raise AttributeDefinitionError, "Attribute already defined: #{name}"
+    end
+
     @attributes << attribute
   end
 
@@ -250,4 +255,8 @@ class Factory
     end
   end
 
+  def attribute_defined? (name)
+    !@attributes.detect {|attr| attr.name == name }.nil?
+  end
+
 end

test/factory_test.rb

@@ -91,6 +91,12 @@ class FactoryTest < Test::Unit::TestCase
       assert_equal @class, @factory.build_class
     end
 
+    should "not allow the same attribute to be added twice" do
+      assert_raise(Factory::AttributeDefinitionError) do
+        2.times { @factory.add_attribute @name }
+      end
+    end
+
     context "when adding an attribute with a value parameter" do
 
       setup do