Fix certain tests not assert correct values for Rails 2.2+

Assert invalid attributes using invalid? rather than checking exactly how many errors there are

test/unit/preference_definition_test.rb

@@ -95,8 +95,8 @@ def test_should_type_cast_to_true_if_value_is_true_string
     assert_equal true, @definition.type_cast('true')
   end
 
-  def test_should_type_cast_to_false_if_value_is_not_true_string
-    assert_equal false, @definition.type_cast('')
+  def test_should_type_cast_to_nil_if_value_is_not_true_string
+    assert_nil @definition.type_cast('')
   end
 
   def test_should_query_false_if_value_is_nil

test/unit/preference_test.rb

@@ -43,19 +43,19 @@ def test_should_be_valid_with_a_set_of_valid_attributes
   def test_should_require_an_attribute
     preference = new_preference(:attribute => nil)
     assert !preference.valid?
-    assert_equal 1, Array(preference.errors.on(:attribute)).size
+    assert preference.errors.invalid?(:attribute)
   end
 
   def test_should_require_an_owner_id
     preference = new_preference(:owner => nil)
     assert !preference.valid?
-    assert_equal 1, Array(preference.errors.on(:owner_id)).size
+    assert preference.errors.invalid?(:owner_id)
   end
 
   def test_should_require_an_owner_type
     preference = new_preference(:owner => nil)
     assert !preference.valid?
-    assert_equal 1, Array(preference.errors.on(:owner_type)).size
+    assert preference.errors.invalid?(:owner_type)
   end
 
   def test_should_not_require_a_group_id
@@ -78,7 +78,7 @@ def test_should_require_a_group_type_if_id_specified
     preference = new_preference(:group => nil)
     preference.group_id = 1
     assert !preference.valid?
-    assert_equal 1, Array(preference.errors.on(:group_type)).size
+    assert preference.errors.invalid?(:group_type)
   end
 
   def test_should_protect_attributes_from_mass_assignment