rails--rails/activerecord/test/cases/dirty_test.rb

# frozen_string_literal: true

require "cases/helper"
require "models/topic"    # For booleans
require "models/pirate"   # For timestamps
require "models/parrot"
require "models/person"   # For optimistic locking
require "models/aircraft"
require "models/numeric_data"

class DirtyTest < ActiveRecord::TestCase
  include InTimeZone

  # Dummy to force column loads so query counts are clean.
  def setup
    Person.create first_name: "foo"
  end

  def test_attribute_changes
    # New record - no changes.
    pirate = Pirate.new
    assert_equal false, pirate.catchphrase_changed?
    assert_equal false, pirate.non_validated_parrot_id_changed?

    # Change catchphrase.
    pirate.catchphrase = "arrr"
    assert_predicate pirate, :catchphrase_changed?
    assert_nil pirate.catchphrase_was
    assert_equal [nil, "arrr"], pirate.catchphrase_change

    # Saved - no changes.
    pirate.save!
    assert_not_predicate pirate, :catchphrase_changed?
    assert_nil pirate.catchphrase_change

    # Same value - no changes.
    pirate.catchphrase = "arrr"
    assert_not_predicate pirate, :catchphrase_changed?
    assert_nil pirate.catchphrase_change
  end

  def test_time_attributes_changes_with_time_zone
    in_time_zone "Paris" do
      target = Class.new(ActiveRecord::Base)
      target.table_name = "pirates"

      # New record - no changes.
      pirate = target.new
      assert_not_predicate pirate, :created_on_changed?
      assert_nil pirate.created_on_change

      # Saved - no changes.
      pirate.catchphrase = "arrrr, time zone!!"
      pirate.save!
      assert_not_predicate pirate, :created_on_changed?
      assert_nil pirate.created_on_change

      # Change created_on.
      old_created_on = pirate.created_on
      pirate.created_on = Time.now - 1.day
      assert_predicate pirate, :created_on_changed?
      assert_kind_of ActiveSupport::TimeWithZone, pirate.created_on_was
      assert_equal old_created_on, pirate.created_on_was
      pirate.created_on = old_created_on
      assert_not_predicate pirate, :created_on_changed?
    end
  end

  def test_setting_time_attributes_with_time_zone_field_to_itself_should_not_be_marked_as_a_change
    in_time_zone "Paris" do
      target = Class.new(ActiveRecord::Base)
      target.table_name = "pirates"

      pirate = target.create!
      pirate.created_on = pirate.created_on
      assert_not_predicate pirate, :created_on_changed?
    end
  end

  def test_time_attributes_changes_without_time_zone_by_skip
    in_time_zone "Paris" do
      target = Class.new(ActiveRecord::Base)
      target.table_name = "pirates"

      target.skip_time_zone_conversion_for_attributes = [:created_on]

      # New record - no changes.
      pirate = target.new
      assert_not_predicate pirate, :created_on_changed?
      assert_nil pirate.created_on_change

      # Saved - no changes.
      pirate.catchphrase = "arrrr, time zone!!"
      pirate.save!
      assert_not_predicate pirate, :created_on_changed?
      assert_nil pirate.created_on_change

      # Change created_on.
      old_created_on = pirate.created_on
      pirate.created_on = Time.now + 1.day
      assert_predicate pirate, :created_on_changed?
      # kind_of does not work because
      # ActiveSupport::TimeWithZone.name == 'Time'
      assert_instance_of Time, pirate.created_on_was
      assert_equal old_created_on, pirate.created_on_was
    end
  end

  def test_time_attributes_changes_without_time_zone
    with_timezone_config aware_attributes: false do
      target = Class.new(ActiveRecord::Base)
      target.table_name = "pirates"

      # New record - no changes.
      pirate = target.new
      assert_not_predicate pirate, :created_on_changed?
      assert_nil pirate.created_on_change

      # Saved - no changes.
      pirate.catchphrase = "arrrr, time zone!!"
      pirate.save!
      assert_not_predicate pirate, :created_on_changed?
      assert_nil pirate.created_on_change

      # Change created_on.
      old_created_on = pirate.created_on
      pirate.created_on = Time.now + 1.day
      assert_predicate pirate, :created_on_changed?
      # kind_of does not work because
      # ActiveSupport::TimeWithZone.name == 'Time'
      assert_instance_of Time, pirate.created_on_was
      assert_equal old_created_on, pirate.created_on_was
    end
  end

  def test_aliased_attribute_changes
    # the actual attribute here is name, title is an
    # alias setup via alias_attribute
    parrot = Parrot.new
    assert_not_predicate parrot, :title_changed?
    assert_nil parrot.title_change

    parrot.name = "Sam"
    assert_predicate parrot, :title_changed?
    assert_nil parrot.title_was
    assert_equal parrot.name_change, parrot.title_change
  end

  def test_restore_attribute!
    pirate = Pirate.create!(catchphrase: "Yar!")
    pirate.catchphrase = "Ahoy!"

    pirate.restore_catchphrase!
    assert_equal "Yar!", pirate.catchphrase
    assert_equal Hash.new, pirate.changes
    assert_not_predicate pirate, :catchphrase_changed?
  end

  def test_nullable_number_not_marked_as_changed_if_new_value_is_blank
    pirate = Pirate.new

    ["", nil].each do |value|
      pirate.parrot_id = value
      assert_not_predicate pirate, :parrot_id_changed?
      assert_nil pirate.parrot_id_change
    end
  end

  def test_nullable_decimal_not_marked_as_changed_if_new_value_is_blank
    numeric_data = NumericData.new

    ["", nil].each do |value|
      numeric_data.bank_balance = value
      assert_not_predicate numeric_data, :bank_balance_changed?
      assert_nil numeric_data.bank_balance_change
    end
  end

  def test_nullable_float_not_marked_as_changed_if_new_value_is_blank
    numeric_data = NumericData.new

    ["", nil].each do |value|
      numeric_data.temperature = value
      assert_not_predicate numeric_data, :temperature_changed?
      assert_nil numeric_data.temperature_change
    end
  end

  def test_nullable_datetime_not_marked_as_changed_if_new_value_is_blank
    in_time_zone "Edinburgh" do
      target = Class.new(ActiveRecord::Base)
      target.table_name = "topics"

      topic = target.create
      assert_nil topic.written_on

      ["", nil].each do |value|
        topic.written_on = value
        assert_nil topic.written_on
        assert_not_predicate topic, :written_on_changed?
      end
    end
  end

  def test_integer_zero_to_string_zero_not_marked_as_changed
    pirate = Pirate.new
    pirate.parrot_id = 0
    pirate.catchphrase = "arrr"
    assert pirate.save!

    assert_not_predicate pirate, :changed?

    pirate.parrot_id = "0"
    assert_not_predicate pirate, :changed?
  end

  def test_integer_zero_to_integer_zero_not_marked_as_changed
    pirate = Pirate.new
    pirate.parrot_id = 0
    pirate.catchphrase = "arrr"
    assert pirate.save!

    assert_not_predicate pirate, :changed?

    pirate.parrot_id = 0
    assert_not_predicate pirate, :changed?
  end

  def test_float_zero_to_string_zero_not_marked_as_changed
    data = NumericData.new temperature: 0.0
    data.save!

    assert_not_predicate data, :changed?

    data.temperature = "0"
    assert_empty data.changes

    data.temperature = "0.0"
    assert_empty data.changes

    data.temperature = "0.00"
    assert_empty data.changes
  end

  def test_zero_to_blank_marked_as_changed
    pirate = Pirate.new
    pirate.catchphrase = "Yarrrr, me hearties"
    pirate.parrot_id = 1
    pirate.save

    # check the change from 1 to ''
    pirate = Pirate.find_by_catchphrase("Yarrrr, me hearties")
    pirate.parrot_id = ""
    assert_predicate pirate, :parrot_id_changed?
    assert_equal([1, nil], pirate.parrot_id_change)
    pirate.save

    # check the change from nil to 0
    pirate = Pirate.find_by_catchphrase("Yarrrr, me hearties")
    pirate.parrot_id = 0
    assert_predicate pirate, :parrot_id_changed?
    assert_equal([nil, 0], pirate.parrot_id_change)
    pirate.save

    # check the change from 0 to ''
    pirate = Pirate.find_by_catchphrase("Yarrrr, me hearties")
    pirate.parrot_id = ""
    assert_predicate pirate, :parrot_id_changed?
    assert_equal([0, nil], pirate.parrot_id_change)
  end

  def test_object_should_be_changed_if_any_attribute_is_changed
    pirate = Pirate.new
    assert_not_predicate pirate, :changed?
    assert_equal [], pirate.changed
    assert_equal Hash.new, pirate.changes

    pirate.catchphrase = "arrr"
    assert_predicate pirate, :changed?
    assert_nil pirate.catchphrase_was
    assert_equal %w(catchphrase), pirate.changed
    assert_equal({ "catchphrase" => [nil, "arrr"] }, pirate.changes)

    pirate.save
    assert_not_predicate pirate, :changed?
    assert_equal [], pirate.changed
    assert_equal Hash.new, pirate.changes
  end

  def test_attribute_will_change!
    pirate = Pirate.create!(catchphrase: "arr")

    assert_not_predicate pirate, :catchphrase_changed?
    assert pirate.catchphrase_will_change!
    assert_predicate pirate, :catchphrase_changed?
    assert_equal ["arr", "arr"], pirate.catchphrase_change

    pirate.catchphrase << " matey!"
    assert_predicate pirate, :catchphrase_changed?
    assert_equal ["arr", "arr matey!"], pirate.catchphrase_change
  end

  def test_virtual_attribute_will_change
    parrot = Parrot.create!(name: "Ruby")
    parrot.send(:attribute_will_change!, :cancel_save_from_callback)
    assert_predicate parrot, :has_changes_to_save?
  end

  def test_association_assignment_changes_foreign_key
    pirate = Pirate.create!(catchphrase: "jarl")
    pirate.parrot = Parrot.create!(name: "Lorre")
    assert_predicate pirate, :changed?
    assert_equal %w(parrot_id), pirate.changed
  end

  def test_attribute_should_be_compared_with_type_cast
    topic = Topic.new
    assert_predicate topic, :approved?
    assert_not_predicate topic, :approved_changed?

    # Coming from web form.
    params = { topic: { approved: 1 } }
    # In the controller.
    topic.attributes = params[:topic]
    assert_predicate topic, :approved?
    assert_not_predicate topic, :approved_changed?
  end

  def test_partial_update
    pirate = Pirate.new(catchphrase: "foo")
    old_updated_on = 1.hour.ago.beginning_of_day

    with_partial_writes Pirate, false do
      assert_queries(2) { 2.times { pirate.save! } }
      Pirate.where(id: pirate.id).update_all(updated_on: old_updated_on)
    end

    with_partial_writes Pirate, true do
      assert_queries(0) { 2.times { pirate.save! } }
      assert_equal old_updated_on, pirate.reload.updated_on

      assert_queries(1) { pirate.catchphrase = "bar"; pirate.save! }
      assert_not_equal old_updated_on, pirate.reload.updated_on
    end
  end

  def test_partial_update_with_optimistic_locking
    person = Person.new(first_name: "foo")

    with_partial_writes Person, false do
      assert_queries(2) { 2.times { person.save! } }
      Person.where(id: person.id).update_all(first_name: "baz")
    end

    old_lock_version = person.lock_version

    with_partial_writes Person, true do
      assert_queries(0) { 2.times { person.save! } }
      assert_equal old_lock_version, person.reload.lock_version

      assert_queries(1) { person.first_name = "bar"; person.save! }
      assert_not_equal old_lock_version, person.reload.lock_version
    end
  end

  def test_changed_attributes_should_be_preserved_if_save_failure
    pirate = Pirate.new
    pirate.parrot_id = 1
    assert !pirate.save
    check_pirate_after_save_failure(pirate)

    pirate = Pirate.new
    pirate.parrot_id = 1
    assert_raise(ActiveRecord::RecordInvalid) { pirate.save! }
    check_pirate_after_save_failure(pirate)
  end

  def test_reload_should_clear_changed_attributes
    pirate = Pirate.create!(catchphrase: "shiver me timbers")
    pirate.catchphrase = "*hic*"
    assert_predicate pirate, :changed?
    pirate.reload
    assert_not_predicate pirate, :changed?
  end

  def test_dup_objects_should_not_copy_dirty_flag_from_creator
    pirate = Pirate.create!(catchphrase: "shiver me timbers")
    pirate_dup = pirate.dup
    pirate_dup.restore_catchphrase!
    pirate.catchphrase = "I love Rum"
    assert_predicate pirate, :catchphrase_changed?
    assert_not_predicate pirate_dup, :catchphrase_changed?
  end

  def test_reverted_changes_are_not_dirty
    phrase = "shiver me timbers"
    pirate = Pirate.create!(catchphrase: phrase)
    pirate.catchphrase = "*hic*"
    assert_predicate pirate, :changed?
    pirate.catchphrase = phrase
    assert_not_predicate pirate, :changed?
  end

  def test_reverted_changes_are_not_dirty_after_multiple_changes
    phrase = "shiver me timbers"
    pirate = Pirate.create!(catchphrase: phrase)
    10.times do |i|
      pirate.catchphrase = "*hic*" * i
      assert_predicate pirate, :changed?
    end
    assert_predicate pirate, :changed?
    pirate.catchphrase = phrase
    assert_not_predicate pirate, :changed?
  end

  def test_reverted_changes_are_not_dirty_going_from_nil_to_value_and_back
    pirate = Pirate.create!(catchphrase: "Yar!")

    pirate.parrot_id = 1
    assert_predicate pirate, :changed?
    assert_predicate pirate, :parrot_id_changed?
    assert_not_predicate pirate, :catchphrase_changed?

    pirate.parrot_id = nil
    assert_not_predicate pirate, :changed?
    assert_not_predicate pirate, :parrot_id_changed?
    assert_not_predicate pirate, :catchphrase_changed?
  end

  def test_save_should_store_serialized_attributes_even_with_partial_writes
    with_partial_writes(Topic) do
      topic = Topic.create!(content: { a: "a" })

      assert_not_predicate topic, :changed?

      topic.content[:b] = "b"

      assert_predicate topic, :changed?

      topic.save!

      assert_not_predicate topic, :changed?
      assert_equal "b", topic.content[:b]

      topic.reload

      assert_equal "b", topic.content[:b]
    end
  end

  def test_save_always_should_update_timestamps_when_serialized_attributes_are_present
    with_partial_writes(Topic) do
      topic = Topic.create!(content: { a: "a" })
      topic.save!

      updated_at = topic.updated_at
      travel(1.second) do
        topic.content[:hello] = "world"
        topic.save!
      end

      assert_not_equal updated_at, topic.updated_at
      assert_equal "world", topic.content[:hello]
    end
  end

  def test_save_should_not_save_serialized_attribute_with_partial_writes_if_not_present
    with_partial_writes(Topic) do
      topic = Topic.create!(author_name: "Bill", content: { a: "a" })
      topic = Topic.select("id, author_name").find(topic.id)
      topic.update_columns author_name: "John"
      assert_not_nil topic.reload.content
    end
  end

  def test_previous_changes
    # original values should be in previous_changes
    pirate = Pirate.new

    assert_equal Hash.new, pirate.previous_changes
    pirate.catchphrase = "arrr"
    pirate.save!

    assert_equal 4, pirate.previous_changes.size
    assert_equal [nil, "arrr"], pirate.previous_changes["catchphrase"]
    assert_equal [nil, pirate.id], pirate.previous_changes["id"]
    assert_nil pirate.previous_changes["updated_on"][0]
    assert_not_nil pirate.previous_changes["updated_on"][1]
    assert_nil pirate.previous_changes["created_on"][0]
    assert_not_nil pirate.previous_changes["created_on"][1]
    assert !pirate.previous_changes.key?("parrot_id")

    # original values should be in previous_changes
    pirate = Pirate.new

    assert_equal Hash.new, pirate.previous_changes
    pirate.catchphrase = "arrr"
    pirate.save

    assert_equal 4, pirate.previous_changes.size
    assert_equal [nil, "arrr"], pirate.previous_changes["catchphrase"]
    assert_equal [nil, pirate.id], pirate.previous_changes["id"]
    assert_includes pirate.previous_changes, "updated_on"
    assert_includes pirate.previous_changes, "created_on"
    assert !pirate.previous_changes.key?("parrot_id")

    pirate.catchphrase = "Yar!!"
    pirate.reload
    assert_equal Hash.new, pirate.previous_changes

    pirate = Pirate.find_by_catchphrase("arrr")

    travel(1.second)

    pirate.catchphrase = "Me Maties!"
    pirate.save!

    assert_equal 2, pirate.previous_changes.size
    assert_equal ["arrr", "Me Maties!"], pirate.previous_changes["catchphrase"]
    assert_not_nil pirate.previous_changes["updated_on"][0]
    assert_not_nil pirate.previous_changes["updated_on"][1]
    assert !pirate.previous_changes.key?("parrot_id")
    assert !pirate.previous_changes.key?("created_on")

    pirate = Pirate.find_by_catchphrase("Me Maties!")

    travel(1.second)

    pirate.catchphrase = "Thar She Blows!"
    pirate.save

    assert_equal 2, pirate.previous_changes.size
    assert_equal ["Me Maties!", "Thar She Blows!"], pirate.previous_changes["catchphrase"]
    assert_not_nil pirate.previous_changes["updated_on"][0]
    assert_not_nil pirate.previous_changes["updated_on"][1]
    assert !pirate.previous_changes.key?("parrot_id")
    assert !pirate.previous_changes.key?("created_on")

    travel(1.second)

    pirate = Pirate.find_by_catchphrase("Thar She Blows!")
    pirate.update(catchphrase: "Ahoy!")

    assert_equal 2, pirate.previous_changes.size
    assert_equal ["Thar She Blows!", "Ahoy!"], pirate.previous_changes["catchphrase"]
    assert_not_nil pirate.previous_changes["updated_on"][0]
    assert_not_nil pirate.previous_changes["updated_on"][1]
    assert !pirate.previous_changes.key?("parrot_id")
    assert !pirate.previous_changes.key?("created_on")

    travel(1.second)

    pirate = Pirate.find_by_catchphrase("Ahoy!")
    pirate.update_attribute(:catchphrase, "Ninjas suck!")

    assert_equal 2, pirate.previous_changes.size
    assert_equal ["Ahoy!", "Ninjas suck!"], pirate.previous_changes["catchphrase"]
    assert_not_nil pirate.previous_changes["updated_on"][0]
    assert_not_nil pirate.previous_changes["updated_on"][1]
    assert !pirate.previous_changes.key?("parrot_id")
    assert !pirate.previous_changes.key?("created_on")
  ensure
    travel_back
  end

  class Testings < ActiveRecord::Base; end
  def test_field_named_field
    ActiveRecord::Base.connection.create_table :testings do |t|
      t.string :field
    end
    assert_nothing_raised do
      Testings.new.attributes
    end
  ensure
    ActiveRecord::Base.connection.drop_table :testings rescue nil
    ActiveRecord::Base.clear_cache!
  end

  def test_datetime_attribute_can_be_updated_with_fractional_seconds
    skip "Fractional seconds are not supported" unless subsecond_precision_supported?
    in_time_zone "Paris" do
      target = Class.new(ActiveRecord::Base)
      target.table_name = "topics"

      written_on = Time.utc(2012, 12, 1, 12, 0, 0).in_time_zone("Paris")

      topic = target.create(written_on: written_on)
      topic.written_on += 0.3

      assert topic.written_on_changed?, "Fractional second update not detected"
    end
  end

  def test_datetime_attribute_doesnt_change_if_zone_is_modified_in_string
    time_in_paris = Time.utc(2014, 1, 1, 12, 0, 0).in_time_zone("Paris")
    pirate = Pirate.create!(catchphrase: "rrrr", created_on: time_in_paris)

    pirate.created_on = pirate.created_on.in_time_zone("Tokyo").to_s
    assert_not_predicate pirate, :created_on_changed?
  end

  test "partial insert" do
    with_partial_writes Person do
      jon = nil
      assert_sql(/first_name/i) do
        jon = Person.create! first_name: "Jon"
      end

      assert ActiveRecord::SQLCounter.log_all.none? { |sql| sql.include?("followers_count") }

      jon.reload
      assert_equal "Jon", jon.first_name
      assert_equal 0, jon.followers_count
      assert_not_nil jon.id
    end
  end

  test "partial insert with empty values" do
    with_partial_writes Aircraft do
      a = Aircraft.create!
      a.reload
      assert_not_nil a.id
    end
  end

  test "in place mutation detection" do
    pirate = Pirate.create!(catchphrase: "arrrr")
    pirate.catchphrase << " matey!"

    assert_predicate pirate, :catchphrase_changed?
    expected_changes = {
      "catchphrase" => ["arrrr", "arrrr matey!"]
    }
    assert_equal(expected_changes, pirate.changes)
    assert_equal("arrrr", pirate.catchphrase_was)
    assert pirate.catchphrase_changed?(from: "arrrr")
    assert_not pirate.catchphrase_changed?(from: "anything else")
    assert_includes pirate.changed_attributes, :catchphrase

    pirate.save!
    pirate.reload

    assert_equal "arrrr matey!", pirate.catchphrase
    assert_not_predicate pirate, :changed?
  end

  test "in place mutation for binary" do
    klass = Class.new(ActiveRecord::Base) do
      self.table_name = :binaries
      serialize :data
    end

    binary = klass.create!(data: "\\\\foo")

    assert_not_predicate binary, :changed?

    binary.data = binary.data.dup

    assert_not_predicate binary, :changed?

    binary = klass.last

    assert_not_predicate binary, :changed?

    binary.data << "bar"

    assert_predicate binary, :changed?
  end

  test "changes is correct for subclass" do
    foo = Class.new(Pirate) do
      def catchphrase
        super.upcase
      end
    end

    pirate = foo.create!(catchphrase: "arrrr")

    new_catchphrase = "arrrr matey!"

    pirate.catchphrase = new_catchphrase
    assert_predicate pirate, :catchphrase_changed?

    expected_changes = {
      "catchphrase" => ["arrrr", new_catchphrase]
    }

    assert_equal new_catchphrase.upcase, pirate.catchphrase
    assert_equal expected_changes, pirate.changes
  end

  test "changes is correct if override attribute reader" do
    pirate = Pirate.create!(catchphrase: "arrrr")
    def pirate.catchphrase
      super.upcase
    end

    new_catchphrase = "arrrr matey!"

    pirate.catchphrase = new_catchphrase
    assert_predicate pirate, :catchphrase_changed?

    expected_changes = {
      "catchphrase" => ["arrrr", new_catchphrase]
    }

    assert_equal new_catchphrase.upcase, pirate.catchphrase
    assert_equal expected_changes, pirate.changes
  end

  test "attribute_changed? doesn't compute in-place changes for unrelated attributes" do
    test_type_class = Class.new(ActiveRecord::Type::Value) do
      define_method(:changed_in_place?) do |*|
        raise
      end
    end
    klass = Class.new(ActiveRecord::Base) do
      self.table_name = "people"
      attribute :foo, test_type_class.new
    end

    model = klass.new(first_name: "Jim")
    assert_predicate model, :first_name_changed?
  end

  test "attribute_will_change! doesn't try to save non-persistable attributes" do
    klass = Class.new(ActiveRecord::Base) do
      self.table_name = "people"
      attribute :non_persisted_attribute, :string
    end

    record = klass.new(first_name: "Sean")
    record.non_persisted_attribute_will_change!

    assert_predicate record, :non_persisted_attribute_changed?
    assert record.save
  end

  test "mutating and then assigning doesn't remove the change" do
    pirate = Pirate.create!(catchphrase: "arrrr")
    pirate.catchphrase << " matey!"
    pirate.catchphrase = "arrrr matey!"

    assert pirate.catchphrase_changed?(from: "arrrr", to: "arrrr matey!")
  end

  test "getters with side effects are allowed" do
    klass = Class.new(Pirate) do
      def catchphrase
        if super.blank?
          update_attribute(:catchphrase, "arr") # what could possibly go wrong?
        end
        super
      end
    end

    pirate = klass.create!(catchphrase: "lol")
    pirate.update_attribute(:catchphrase, nil)

    assert_equal "arr", pirate.catchphrase
  end

  test "attributes assigned but not selected are dirty" do
    person = Person.select(:id).first
    assert_not_predicate person, :changed?

    person.first_name = "Sean"
    assert_predicate person, :changed?

    person.first_name = nil
    assert_predicate person, :changed?
  end

  test "attributes not selected are still missing after save" do
    person = Person.select(:id).first
    assert_raises(ActiveModel::MissingAttributeError) { person.first_name }
    assert person.save # calls forget_attribute_assignments
    assert_raises(ActiveModel::MissingAttributeError) { person.first_name }
  end

  test "saved_change_to_attribute? returns whether a change occurred in the last save" do
    person = Person.create!(first_name: "Sean")

    assert_predicate person, :saved_change_to_first_name?
    assert_not_predicate person, :saved_change_to_gender?
    assert person.saved_change_to_first_name?(from: nil, to: "Sean")
    assert person.saved_change_to_first_name?(from: nil)
    assert person.saved_change_to_first_name?(to: "Sean")
    assert_not person.saved_change_to_first_name?(from: "Jim", to: "Sean")
    assert_not person.saved_change_to_first_name?(from: "Jim")
    assert_not person.saved_change_to_first_name?(to: "Jim")
  end

  test "saved_change_to_attribute returns the change that occurred in the last save" do
    person = Person.create!(first_name: "Sean", gender: "M")

    assert_equal [nil, "Sean"], person.saved_change_to_first_name
    assert_equal [nil, "M"], person.saved_change_to_gender

    person.update(first_name: "Jim")

    assert_equal ["Sean", "Jim"], person.saved_change_to_first_name
    assert_nil person.saved_change_to_gender
  end

  test "attribute_before_last_save returns the original value before saving" do
    person = Person.create!(first_name: "Sean", gender: "M")

    assert_nil person.first_name_before_last_save
    assert_nil person.gender_before_last_save

    person.first_name = "Jim"

    assert_nil person.first_name_before_last_save
    assert_nil person.gender_before_last_save

    person.save

    assert_equal "Sean", person.first_name_before_last_save
    assert_equal "M", person.gender_before_last_save
  end

  test "saved_changes? returns whether the last call to save changed anything" do
    person = Person.create!(first_name: "Sean")

    assert_predicate person, :saved_changes?

    person.save

    assert_not_predicate person, :saved_changes?
  end

  test "saved_changes returns a hash of all the changes that occurred" do
    person = Person.create!(first_name: "Sean", gender: "M")

    assert_equal [nil, "Sean"], person.saved_changes[:first_name]
    assert_equal [nil, "M"], person.saved_changes[:gender]
    assert_equal %w(id first_name gender created_at updated_at).sort, person.saved_changes.keys.sort

    travel(1.second) do
      person.update(first_name: "Jim")
    end

    assert_equal ["Sean", "Jim"], person.saved_changes[:first_name]
    assert_equal %w(first_name lock_version updated_at).sort, person.saved_changes.keys.sort
  end

  test "changed? in after callbacks returns false" do
    klass = Class.new(ActiveRecord::Base) do
      self.table_name = "people"

      after_save do
        raise "changed? should be false" if changed?
        raise "has_changes_to_save? should be false" if has_changes_to_save?
        raise "saved_changes? should be true" unless saved_changes?
      end
    end

    person = klass.create!(first_name: "Sean")
    assert_not_predicate person, :changed?
  end

  private
    def with_partial_writes(klass, on = true)
      old = klass.partial_writes?
      klass.partial_writes = on
      yield
    ensure
      klass.partial_writes = old
    end

    def check_pirate_after_save_failure(pirate)
      assert_predicate pirate, :changed?
      assert_predicate pirate, :parrot_id_changed?
      assert_equal %w(parrot_id), pirate.changed
      assert_nil pirate.parrot_id_was
    end
end