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

# frozen_string_literal: true

require "cases/helper"
require "models/topic"
require "models/reply"
require "models/developer"
require "models/computer"
require "models/book"
require "models/author"
require "models/post"
require "models/movie"

class TransactionTest < ActiveRecord::TestCase
  self.use_transactional_tests = false
  fixtures :topics, :developers, :authors, :author_addresses, :posts

  def setup
    @first, @second = Topic.find(1, 2).sort_by(&:id)
  end

  def test_persisted_in_a_model_with_custom_primary_key_after_failed_save
    movie = Movie.create
    assert_not_predicate movie, :persisted?
  end

  def test_raise_after_destroy
    assert_not_predicate @first, :frozen?

    assert_raises(RuntimeError) {
      Topic.transaction do
        @first.destroy
        assert_predicate @first, :frozen?
        raise
      end
    }

    assert @first.reload
    assert_not_predicate @first, :frozen?
  end

  def test_successful
    Topic.transaction do
      @first.approved  = true
      @second.approved = false
      @first.save
      @second.save
    end

    assert Topic.find(1).approved?, "First should have been approved"
    assert !Topic.find(2).approved?, "Second should have been unapproved"
  end

  def transaction_with_return
    Topic.transaction do
      @first.approved  = true
      @second.approved = false
      @first.save
      @second.save
      return
    end
  end

  def test_add_to_null_transaction
    topic = Topic.new
    topic.add_to_transaction
  end

  def test_successful_with_return
    committed = false

    Topic.connection.class_eval do
      alias :real_commit_db_transaction :commit_db_transaction
      define_method(:commit_db_transaction) do
        committed = true
        real_commit_db_transaction
      end
    end

    transaction_with_return
    assert committed

    assert Topic.find(1).approved?, "First should have been approved"
    assert !Topic.find(2).approved?, "Second should have been unapproved"
  ensure
    Topic.connection.class_eval do
      remove_method :commit_db_transaction
      alias :commit_db_transaction :real_commit_db_transaction rescue nil
    end
  end

  def test_number_of_transactions_in_commit
    num = nil

    Topic.connection.class_eval do
      alias :real_commit_db_transaction :commit_db_transaction
      define_method(:commit_db_transaction) do
        num = transaction_manager.open_transactions
        real_commit_db_transaction
      end
    end

    Topic.transaction do
      @first.approved = true
      @first.save!
    end

    assert_equal 0, num
  ensure
    Topic.connection.class_eval do
      remove_method :commit_db_transaction
      alias :commit_db_transaction :real_commit_db_transaction rescue nil
    end
  end

  def test_successful_with_instance_method
    @first.transaction do
      @first.approved  = true
      @second.approved = false
      @first.save
      @second.save
    end

    assert Topic.find(1).approved?, "First should have been approved"
    assert !Topic.find(2).approved?, "Second should have been unapproved"
  end

  def test_failing_on_exception
    begin
      Topic.transaction do
        @first.approved  = true
        @second.approved = false
        @first.save
        @second.save
        raise "Bad things!"
      end
    rescue
      # caught it
    end

    assert @first.approved?, "First should still be changed in the objects"
    assert !@second.approved?, "Second should still be changed in the objects"

    assert !Topic.find(1).approved?, "First shouldn't have been approved"
    assert Topic.find(2).approved?, "Second should still be approved"
  end

  def test_raising_exception_in_callback_rollbacks_in_save
    def @first.after_save_for_transaction
      raise "Make the transaction rollback"
    end

    @first.approved = true
    e = assert_raises(RuntimeError) { @first.save }
    assert_equal "Make the transaction rollback", e.message
    assert_not_predicate Topic.find(1), :approved?
  end

  def test_rolling_back_in_a_callback_rollbacks_before_save
    def @first.before_save_for_transaction
      raise ActiveRecord::Rollback
    end
    assert !@first.approved

    Topic.transaction do
      @first.approved = true
      @first.save!
    end
    assert !Topic.find(@first.id).approved?, "Should not commit the approved flag"
  end

  def test_raising_exception_in_nested_transaction_restore_state_in_save
    topic = Topic.new

    def topic.after_save_for_transaction
      raise "Make the transaction rollback"
    end

    assert_raises(RuntimeError) do
      Topic.transaction { topic.save }
    end

    assert topic.new_record?, "#{topic.inspect} should be new record"
  end

  def test_transaction_state_is_cleared_when_record_is_persisted
    author = Author.create! name: "foo"
    author.name = nil
    assert_not author.save
    assert_not_predicate author, :new_record?
  end

  def test_update_should_rollback_on_failure
    author = Author.find(1)
    posts_count = author.posts.size
    assert posts_count > 0
    status = author.update(name: nil, post_ids: [])
    assert !status
    assert_equal posts_count, author.posts.reload.size
  end

  def test_update_should_rollback_on_failure!
    author = Author.find(1)
    posts_count = author.posts.size
    assert posts_count > 0
    assert_raise(ActiveRecord::RecordInvalid) do
      author.update!(name: nil, post_ids: [])
    end
    assert_equal posts_count, author.posts.reload.size
  end

  def test_cancellation_from_before_destroy_rollbacks_in_destroy
    add_cancelling_before_destroy_with_db_side_effect_to_topic @first
    nbooks_before_destroy = Book.count
    status = @first.destroy
    assert !status
    @first.reload
    assert_equal nbooks_before_destroy, Book.count
  end

  %w(validation save).each do |filter|
    define_method("test_cancellation_from_before_filters_rollbacks_in_#{filter}") do
      send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic", @first)
      nbooks_before_save = Book.count
      original_author_name = @first.author_name
      @first.author_name += "_this_should_not_end_up_in_the_db"
      status = @first.save
      assert !status
      assert_equal original_author_name, @first.reload.author_name
      assert_equal nbooks_before_save, Book.count
    end

    define_method("test_cancellation_from_before_filters_rollbacks_in_#{filter}!") do
      send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic", @first)
      nbooks_before_save = Book.count
      original_author_name = @first.author_name
      @first.author_name += "_this_should_not_end_up_in_the_db"

      begin
        @first.save!
      rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotSaved
      end

      assert_equal original_author_name, @first.reload.author_name
      assert_equal nbooks_before_save, Book.count
    end
  end

  def test_callback_rollback_in_create
    topic = Class.new(Topic) {
      def after_create_for_transaction
        raise "Make the transaction rollback"
      end
    }

    new_topic = topic.new(title: "A new topic",
                          author_name: "Ben",
                          author_email_address: "ben@example.com",
                          written_on: "2003-07-16t15:28:11.2233+01:00",
                          last_read: "2004-04-15",
                          bonus_time: "2005-01-30t15:28:00.00+01:00",
                          content: "Have a nice day",
                          approved: false)

    new_record_snapshot = !new_topic.persisted?
    id_present = new_topic.has_attribute?(Topic.primary_key)
    id_snapshot = new_topic.id

    # Make sure the second save gets the after_create callback called.
    2.times do
      new_topic.approved = true
      e = assert_raises(RuntimeError) { new_topic.save }
      assert_equal "Make the transaction rollback", e.message
      assert_equal new_record_snapshot, !new_topic.persisted?, "The topic should have its old persisted value"
      if id_snapshot.nil?
        assert_nil new_topic.id, "The topic should have its old id"
      else
        assert_equal id_snapshot, new_topic.id, "The topic should have its old id"
      end
      assert_equal id_present, new_topic.has_attribute?(Topic.primary_key)
    end
  end

  def test_callback_rollback_in_create_with_record_invalid_exception
    topic = Class.new(Topic) {
      def after_create_for_transaction
        raise ActiveRecord::RecordInvalid.new(Author.new)
      end
    }

    new_topic = topic.create(title: "A new topic")
    assert !new_topic.persisted?, "The topic should not be persisted"
    assert_nil new_topic.id, "The topic should not have an ID"
  end

  def test_nested_explicit_transactions
    Topic.transaction do
      Topic.transaction do
        @first.approved  = true
        @second.approved = false
        @first.save
        @second.save
      end
    end

    assert Topic.find(1).approved?, "First should have been approved"
    assert !Topic.find(2).approved?, "Second should have been unapproved"
  end

  def test_nested_transaction_with_new_transaction_applies_parent_state_on_rollback
    topic_one = Topic.new(title: "A new topic")
    topic_two = Topic.new(title: "Another new topic")

    Topic.transaction do
      topic_one.save

      Topic.transaction(requires_new: true) do
        topic_two.save

        assert_predicate topic_one, :persisted?
        assert_predicate topic_two, :persisted?
      end

      raise ActiveRecord::Rollback
    end

    refute_predicate topic_one, :persisted?
    refute_predicate topic_two, :persisted?
  end

  def test_nested_transaction_without_new_transaction_applies_parent_state_on_rollback
    topic_one = Topic.new(title: "A new topic")
    topic_two = Topic.new(title: "Another new topic")

    Topic.transaction do
      topic_one.save

      Topic.transaction do
        topic_two.save

        assert_predicate topic_one, :persisted?
        assert_predicate topic_two, :persisted?
      end

      raise ActiveRecord::Rollback
    end

    refute_predicate topic_one, :persisted?
    refute_predicate topic_two, :persisted?
  end

  def test_double_nested_transaction_applies_parent_state_on_rollback
    topic_one = Topic.new(title: "A new topic")
    topic_two = Topic.new(title: "Another new topic")
    topic_three = Topic.new(title: "Another new topic of course")

    Topic.transaction do
      topic_one.save

      Topic.transaction do
        topic_two.save

        Topic.transaction do
          topic_three.save
        end
      end

      assert_predicate topic_one, :persisted?
      assert_predicate topic_two, :persisted?
      assert_predicate topic_three, :persisted?

      raise ActiveRecord::Rollback
    end

    refute_predicate topic_one, :persisted?
    refute_predicate topic_two, :persisted?
    refute_predicate topic_three, :persisted?
  end

  def test_manually_rolling_back_a_transaction
    Topic.transaction do
      @first.approved  = true
      @second.approved = false
      @first.save
      @second.save

      raise ActiveRecord::Rollback
    end

    assert @first.approved?, "First should still be changed in the objects"
    assert !@second.approved?, "Second should still be changed in the objects"

    assert !Topic.find(1).approved?, "First shouldn't have been approved"
    assert Topic.find(2).approved?, "Second should still be approved"
  end

  def test_invalid_keys_for_transaction
    assert_raise ArgumentError do
      Topic.transaction nested: true do
      end
    end
  end

  def test_force_savepoint_in_nested_transaction
    Topic.transaction do
      @first.approved = true
      @second.approved = false
      @first.save!
      @second.save!

      begin
        Topic.transaction requires_new: true do
          @first.happy = false
          @first.save!
          raise
        end
      rescue
      end
    end

    assert_predicate @first.reload, :approved?
    assert_not_predicate @second.reload, :approved?
  end if Topic.connection.supports_savepoints?

  def test_force_savepoint_on_instance
    @first.transaction do
      @first.approved  = true
      @second.approved = false
      @first.save!
      @second.save!

      begin
        @second.transaction requires_new: true do
          @first.happy = false
          @first.save!
          raise
        end
      rescue
      end
    end

    assert_predicate @first.reload, :approved?
    assert_not_predicate @second.reload, :approved?
  end if Topic.connection.supports_savepoints?

  def test_no_savepoint_in_nested_transaction_without_force
    Topic.transaction do
      @first.approved = true
      @second.approved = false
      @first.save!
      @second.save!

      begin
        Topic.transaction do
          @first.approved = false
          @first.save!
          raise
        end
      rescue
      end
    end

    assert_not_predicate @first.reload, :approved?
    assert_not_predicate @second.reload, :approved?
  end if Topic.connection.supports_savepoints?

  def test_many_savepoints
    Topic.transaction do
      @first.content = "One"
      @first.save!

      begin
        Topic.transaction requires_new: true do
          @first.content = "Two"
          @first.save!

          begin
            Topic.transaction requires_new: true do
              @first.content = "Three"
              @first.save!

              begin
                Topic.transaction requires_new: true do
                  @first.content = "Four"
                  @first.save!
                  raise
                end
              rescue
              end

              @three = @first.reload.content
              raise
            end
          rescue
          end

          @two = @first.reload.content
          raise
        end
      rescue
      end

      @one = @first.reload.content
    end

    assert_equal "One", @one
    assert_equal "Two", @two
    assert_equal "Three", @three
  end if Topic.connection.supports_savepoints?

  def test_using_named_savepoints
    Topic.transaction do
      @first.approved = true
      @first.save!
      Topic.connection.create_savepoint("first")

      @first.approved = false
      @first.save!
      Topic.connection.rollback_to_savepoint("first")
      assert_predicate @first.reload, :approved?

      @first.approved = false
      @first.save!
      Topic.connection.release_savepoint("first")
      assert_not_predicate @first.reload, :approved?
    end
  end if Topic.connection.supports_savepoints?

  def test_releasing_named_savepoints
    Topic.transaction do
      Topic.connection.create_savepoint("another")
      Topic.connection.release_savepoint("another")

      # The savepoint is now gone and we can't remove it again.
      assert_raises(ActiveRecord::StatementInvalid) do
        Topic.connection.release_savepoint("another")
      end
    end
  end

  def test_savepoints_name
    Topic.transaction do
      assert_nil Topic.connection.current_savepoint_name
      assert_nil Topic.connection.current_transaction.savepoint_name

      Topic.transaction(requires_new: true) do
        assert_equal "active_record_1", Topic.connection.current_savepoint_name
        assert_equal "active_record_1", Topic.connection.current_transaction.savepoint_name

        Topic.transaction(requires_new: true) do
          assert_equal "active_record_2", Topic.connection.current_savepoint_name
          assert_equal "active_record_2", Topic.connection.current_transaction.savepoint_name
        end

        assert_equal "active_record_1", Topic.connection.current_savepoint_name
        assert_equal "active_record_1", Topic.connection.current_transaction.savepoint_name
      end
    end
  end

  def test_rollback_when_commit_raises
    assert_called(Topic.connection, :begin_db_transaction) do
      Topic.connection.stub(:commit_db_transaction, -> { raise("OH NOES") }) do
        assert_called(Topic.connection, :rollback_db_transaction) do

          e = assert_raise RuntimeError do
            Topic.transaction do
              # do nothing
            end
          end
          assert_equal "OH NOES", e.message
        end
      end
    end
  end

  def test_rollback_when_saving_a_frozen_record
    topic = Topic.new(title: "test")
    topic.freeze
    e = assert_raise(frozen_error_class) { topic.save }
    # Not good enough, but we can't do much
    # about it since there is no specific error
    # for frozen objects.
    assert_match(/frozen/i, e.message)
    assert !topic.persisted?, "not persisted"
    assert_nil topic.id
    assert topic.frozen?, "not frozen"
  end

  def test_rollback_when_thread_killed
    return if in_memory_db?

    queue = Queue.new
    thread = Thread.new do
      Topic.transaction do
        @first.approved  = true
        @second.approved = false
        @first.save

        queue.push nil
        sleep

        @second.save
      end
    end

    queue.pop
    thread.kill
    thread.join

    assert @first.approved?, "First should still be changed in the objects"
    assert !@second.approved?, "Second should still be changed in the objects"

    assert !Topic.find(1).approved?, "First shouldn't have been approved"
    assert Topic.find(2).approved?, "Second should still be approved"
  end

  def test_restore_active_record_state_for_all_records_in_a_transaction
    topic_without_callbacks = Class.new(ActiveRecord::Base) do
      self.table_name = "topics"
    end

    topic_1 = Topic.new(title: "test_1")
    topic_2 = Topic.new(title: "test_2")
    topic_3 = topic_without_callbacks.new(title: "test_3")

    Topic.transaction do
      assert topic_1.save
      assert topic_2.save
      assert topic_3.save
      @first.save
      @second.destroy
      assert topic_1.persisted?, "persisted"
      assert_not_nil topic_1.id
      assert topic_2.persisted?, "persisted"
      assert_not_nil topic_2.id
      assert topic_3.persisted?, "persisted"
      assert_not_nil topic_3.id
      assert @first.persisted?, "persisted"
      assert_not_nil @first.id
      assert @second.destroyed?, "destroyed"
      raise ActiveRecord::Rollback
    end

    assert !topic_1.persisted?, "not persisted"
    assert_nil topic_1.id
    assert !topic_2.persisted?, "not persisted"
    assert_nil topic_2.id
    assert !topic_3.persisted?, "not persisted"
    assert_nil topic_3.id
    assert @first.persisted?, "persisted"
    assert_not_nil @first.id
    assert !@second.destroyed?, "not destroyed"
  end

  def test_restore_frozen_state_after_double_destroy
    topic = Topic.create
    reply = topic.replies.create

    Topic.transaction do
      topic.destroy # calls #destroy on reply (since dependent: destroy)
      reply.destroy

      raise ActiveRecord::Rollback
    end

    assert_not_predicate reply, :frozen?
    assert_not_predicate topic, :frozen?
  end

  def test_restore_id_after_rollback
    topic = Topic.new

    Topic.transaction do
      topic.save!
      raise ActiveRecord::Rollback
    end

    assert_nil topic.id
  end

  def test_restore_custom_primary_key_after_rollback
    movie = Movie.new(name: "foo")

    Movie.transaction do
      movie.save!
      raise ActiveRecord::Rollback
    end

    assert_nil movie.movieid
  end

  def test_assign_id_after_rollback
    topic = Topic.create!

    Topic.transaction do
      topic.save!
      raise ActiveRecord::Rollback
    end

    topic.id = nil
    assert_nil topic.id
  end

  def test_assign_custom_primary_key_after_rollback
    movie = Movie.create!(name: "foo")

    Movie.transaction do
      movie.save!
      raise ActiveRecord::Rollback
    end

    movie.movieid = nil
    assert_nil movie.movieid
  end

  def test_read_attribute_after_rollback
    topic = Topic.new

    Topic.transaction do
      topic.save!
      raise ActiveRecord::Rollback
    end

    assert_nil topic.read_attribute(:id)
  end

  def test_read_attribute_with_custom_primary_key_after_rollback
    movie = Movie.new(name: "foo")

    Movie.transaction do
      movie.save!
      raise ActiveRecord::Rollback
    end

    assert_nil movie.read_attribute(:movieid)
  end

  def test_write_attribute_after_rollback
    topic = Topic.create!

    Topic.transaction do
      topic.save!
      raise ActiveRecord::Rollback
    end

    topic.write_attribute(:id, nil)
    assert_nil topic.id
  end

  def test_write_attribute_with_custom_primary_key_after_rollback
    movie = Movie.create!(name: "foo")

    Movie.transaction do
      movie.save!
      raise ActiveRecord::Rollback
    end

    movie.write_attribute(:movieid, nil)
    assert_nil movie.movieid
  end

  def test_rollback_of_frozen_records
    topic = Topic.create.freeze
    Topic.transaction do
      topic.destroy
      raise ActiveRecord::Rollback
    end
    assert topic.frozen?, "frozen"
  end

  def test_rollback_for_freshly_persisted_records
    topic = Topic.create
    Topic.transaction do
      topic.destroy
      raise ActiveRecord::Rollback
    end
    assert topic.persisted?, "persisted"
  end

  def test_sqlite_add_column_in_transaction
    return true unless current_adapter?(:SQLite3Adapter)

    # Test first if column creation/deletion works correctly when no
    # transaction is in place.
    #
    # We go back to the connection for the column queries because
    # Topic.columns is cached and won't report changes to the DB

    assert_nothing_raised do
      Topic.reset_column_information
      Topic.connection.add_column("topics", "stuff", :string)
      assert_includes Topic.column_names, "stuff"

      Topic.reset_column_information
      Topic.connection.remove_column("topics", "stuff")
      assert_not_includes Topic.column_names, "stuff"
    end

    if Topic.connection.supports_ddl_transactions?
      assert_nothing_raised do
        Topic.transaction { Topic.connection.add_column("topics", "stuff", :string) }
      end
    else
      Topic.transaction do
        assert_raise(ActiveRecord::StatementInvalid) { Topic.connection.add_column("topics", "stuff", :string) }
        raise ActiveRecord::Rollback
      end
    end
  ensure
    begin
      Topic.connection.remove_column("topics", "stuff")
    rescue
    ensure
      Topic.reset_column_information
    end
  end

  def test_transactions_state_from_rollback
    connection = Topic.connection
    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction

    assert_predicate transaction, :open?
    assert_not_predicate transaction.state, :rolledback?
    assert_not_predicate transaction.state, :committed?

    transaction.rollback

    assert_predicate transaction.state, :rolledback?
    assert_not_predicate transaction.state, :committed?
  end

  def test_transactions_state_from_commit
    connection = Topic.connection
    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction

    assert_predicate transaction, :open?
    assert_not_predicate transaction.state, :rolledback?
    assert_not_predicate transaction.state, :committed?

    transaction.commit

    assert_not_predicate transaction.state, :rolledback?
    assert_predicate transaction.state, :committed?
  end

  def test_set_state_method_is_deprecated
    connection = Topic.connection
    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction

    transaction.commit

    assert_deprecated do
      transaction.state.set_state(:rolledback)
    end
  end

  def test_mark_transaction_state_as_committed
    connection = Topic.connection
    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction

    transaction.rollback

    assert_equal :committed, transaction.state.commit!
  end

  def test_mark_transaction_state_as_rolledback
    connection = Topic.connection
    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction

    transaction.commit

    assert_equal :rolledback, transaction.state.rollback!
  end

  def test_mark_transaction_state_as_nil
    connection = Topic.connection
    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction

    transaction.commit

    assert_nil transaction.state.nullify!
  end

  def test_transaction_rollback_with_primarykeyless_tables
    connection = ActiveRecord::Base.connection
    connection.create_table(:transaction_without_primary_keys, force: true, id: false) do |t|
      t.integer :thing_id
    end

    klass = Class.new(ActiveRecord::Base) do
      self.table_name = "transaction_without_primary_keys"
      after_commit {} # necessary to trigger the has_transactional_callbacks branch
    end

    assert_no_difference(-> { klass.count }) do
      ActiveRecord::Base.transaction do
        klass.create!
        raise ActiveRecord::Rollback
      end
    end
  ensure
    connection.drop_table "transaction_without_primary_keys", if_exists: true
  end

  private

    %w(validation save destroy).each do |filter|
      define_method("add_cancelling_before_#{filter}_with_db_side_effect_to_topic") do |topic|
        meta = class << topic; self; end
        meta.send("define_method", "before_#{filter}_for_transaction") do
          Book.create
          throw(:abort)
        end
      end
    end
end

class TransactionsWithTransactionalFixturesTest < ActiveRecord::TestCase
  self.use_transactional_tests = true
  fixtures :topics

  def test_automatic_savepoint_in_outer_transaction
    @first = Topic.find(1)

    begin
      Topic.transaction do
        @first.approved = true
        @first.save!
        raise
      end
    rescue
      assert_not_predicate @first.reload, :approved?
    end
  end

  def test_no_automatic_savepoint_for_inner_transaction
    @first = Topic.find(1)

    Topic.transaction do
      @first.approved = true
      @first.save!

      begin
        Topic.transaction do
          @first.approved = false
          @first.save!
          raise
        end
      rescue
      end
    end

    assert_not_predicate @first.reload, :approved?
  end
end if Topic.connection.supports_savepoints?

if ActiveRecord::Base.connection.supports_transaction_isolation?
  class ConcurrentTransactionTest < TransactionTest
    # This will cause transactions to overlap and fail unless they are performed on
    # separate database connections.
    def test_transaction_per_thread
      threads = 3.times.map do
        Thread.new do
          Topic.transaction do
            topic = Topic.find(1)
            topic.approved = !topic.approved?
            assert topic.save!
            topic.approved = !topic.approved?
            assert topic.save!
          end
          Topic.connection.close
        end
      end

      threads.each(&:join)
    end

    # Test for dirty reads among simultaneous transactions.
    def test_transaction_isolation__read_committed
      # Should be invariant.
      original_salary = Developer.find(1).salary
      temporary_salary = 200000

      assert_nothing_raised do
        threads = (1..3).map do
          Thread.new do
            Developer.transaction do
              # Expect original salary.
              dev = Developer.find(1)
              assert_equal original_salary, dev.salary

              dev.salary = temporary_salary
              dev.save!

              # Expect temporary salary.
              dev = Developer.find(1)
              assert_equal temporary_salary, dev.salary

              dev.salary = original_salary
              dev.save!

              # Expect original salary.
              dev = Developer.find(1)
              assert_equal original_salary, dev.salary
            end
            Developer.connection.close
          end
        end

        # Keep our eyes peeled.
        threads << Thread.new do
          10.times do
            sleep 0.05
            Developer.transaction do
              # Always expect original salary.
              assert_equal original_salary, Developer.find(1).salary
            end
          end
          Developer.connection.close
        end

        threads.each(&:join)
      end

      assert_equal original_salary, Developer.find(1).salary
    end
  end
end