7 files changed, 18 insertions, 10 deletions
diff --git a/activemodel/lib/active_model/attribute_mutation_tracker.rb b/activemodel/lib/active_model/attribute_mutation_tracker.rb
index 493be5bb88..6abf37bd44 100644
--- a/activemodel/lib/active_model/attribute_mutation_tracker.rb
+++ b/activemodel/lib/active_model/attribute_mutation_tracker.rb
@@ -11,6 +11,10 @@ module ActiveModel
       @forced_changes = Set.new
     end
 
+    def changed_attribute_names
+      attr_names.select { |attr_name| changed?(attr_name) }
+    end
+
     def changed_values
       attr_names.each_with_object({}.with_indifferent_access) do |attr_name, result|
         if changed?(attr_name)
@@ -23,7 +27,7 @@ module ActiveModel
       attr_names.each_with_object({}.with_indifferent_access) do |attr_name, result|
         change = change_to_attribute(attr_name)
         if change
-          result[attr_name] = change
+          result.merge!(attr_name => change)
         end
       end
     end
@@ -76,6 +80,10 @@ module ActiveModel
   class NullMutationTracker # :nodoc:
     include Singleton
 
+    def changed_attribute_names(*)
+      []
+    end
+
     def changed_values(*)
       {}
     end
diff --git a/activemodel/lib/active_model/validations/inclusion.rb b/activemodel/lib/active_model/validations/inclusion.rb
index 3104e7e329..9c12dc14c5 100644
--- a/activemodel/lib/active_model/validations/inclusion.rb
+++ b/activemodel/lib/active_model/validations/inclusion.rb
@@ -19,7 +19,7 @@ module ActiveModel
       # particular enumerable object.
       #
       #   class Person < ActiveRecord::Base
-      #     validates_inclusion_of :gender, in: %w( m f )
+      #     validates_inclusion_of :role, in: %w( admin contributor )
       #     validates_inclusion_of :age, in: 0..99
       #     validates_inclusion_of :format, in: %w( jpg gif png ), message: "extension %{value} is not included in the list"
       #     validates_inclusion_of :states, in: ->(person) { STATES[person.country] }
diff --git a/activemodel/lib/active_model/validations/validates.rb b/activemodel/lib/active_model/validations/validates.rb
index e28e7e9219..88cca318ef 100644
--- a/activemodel/lib/active_model/validations/validates.rb
+++ b/activemodel/lib/active_model/validations/validates.rb
@@ -63,7 +63,7 @@ module ActiveModel
       # and strings in shortcut form.
       #
       #   validates :email, format: /@/
-      #   validates :gender, inclusion: %w(male female)
+      #   validates :role, inclusion: %(admin contributor)
       #   validates :password, length: 6..20
       #
       # When using shortcut form, ranges and arrays are passed to your
diff --git a/activemodel/test/cases/attributes_dirty_test.rb b/activemodel/test/cases/attributes_dirty_test.rb
index c991176389..f9693a23cd 100644
--- a/activemodel/test/cases/attributes_dirty_test.rb
+++ b/activemodel/test/cases/attributes_dirty_test.rb
@@ -39,7 +39,7 @@ class AttributesDirtyTest < ActiveModel::TestCase
   end
 
   test "changes to attribute values" do
-    assert !@model.changes["name"]
+    assert_not @model.changes["name"]
     @model.name = "John"
     assert_equal [nil, "John"], @model.changes["name"]
   end
diff --git a/activemodel/test/cases/dirty_test.rb b/activemodel/test/cases/dirty_test.rb
index f769eb0da1..b120e68027 100644
--- a/activemodel/test/cases/dirty_test.rb
+++ b/activemodel/test/cases/dirty_test.rb
@@ -78,7 +78,7 @@ class DirtyTest < ActiveModel::TestCase
   end
 
   test "changes to attribute values" do
-    assert !@model.changes["name"]
+    assert_not @model.changes["name"]
     @model.name = "John"
     assert_equal [nil, "John"], @model.changes["name"]
   end
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index cb6a8c43d5..6ff3be1308 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -207,26 +207,26 @@ class ErrorsTest < ActiveModel::TestCase
 
   test "added? returns false when no errors are present" do
     person = Person.new
-    assert !person.errors.added?(:name)
+    assert_not person.errors.added?(:name)
   end
 
   test "added? returns false when checking a nonexisting error and other errors are present for the given attribute" do
     person = Person.new
     person.errors.add(:name, "is invalid")
-    assert !person.errors.added?(:name, "cannot be blank")
+    assert_not person.errors.added?(:name, "cannot be blank")
   end
 
   test "added? returns false when checking for an error, but not providing message arguments" do
     person = Person.new
     person.errors.add(:name, "cannot be blank")
-    assert !person.errors.added?(:name)
+    assert_not person.errors.added?(:name)
   end
 
   test "added? returns false when checking for an error by symbol and a different error with same message is present" do
     I18n.backend.store_translations("en", errors: { attributes: { name: { wrong: "is wrong", used: "is wrong" } } })
     person = Person.new
     person.errors.add(:name, :wrong)
-    assert !person.errors.added?(:name, :used)
+    assert_not person.errors.added?(:name, :used)
   end
 
   test "size calculates the number of error messages" do
diff --git a/activemodel/test/cases/secure_password_test.rb b/activemodel/test/cases/secure_password_test.rb
index d19e81a119..912cb6d5ab 100644
--- a/activemodel/test/cases/secure_password_test.rb
+++ b/activemodel/test/cases/secure_password_test.rb
@@ -187,7 +187,7 @@ class SecurePasswordTest < ActiveModel::TestCase
   test "authenticate" do
     @user.password = "secret"
 
-    assert !@user.authenticate("wrong")
+    assert_not @user.authenticate("wrong")
     assert @user.authenticate("secret")
   end