# File activerecord/lib/active_record/fixtures.rb, line 1022
def enlist_fixture_connections
  ActiveRecord::Base.connection_handler.connection_pool_list.map(&:connection)
end

# File activerecord/lib/active_record/fixtures.rb, line 945
def run_in_transaction?
  use_transactional_tests &&
    !self.class.uses_transaction?(method_name)
end

# File activerecord/lib/active_record/fixtures.rb, line 950
def setup_fixtures(config = ActiveRecord::Base)
  if pre_loaded_fixtures && !use_transactional_tests
    raise RuntimeError, "pre_loaded_fixtures requires use_transactional_tests"
  end

  @fixture_cache = {}
  @fixture_connections = []
  @@already_loaded_fixtures ||= {}
  @connection_subscriber = nil

  # Load fixtures once and begin transaction.
  if run_in_transaction?
    if @@already_loaded_fixtures[self.class]
      @loaded_fixtures = @@already_loaded_fixtures[self.class]
    else
      @loaded_fixtures = load_fixtures(config)
      @@already_loaded_fixtures[self.class] = @loaded_fixtures
    end

    # Begin transactions for connections already established
    @fixture_connections = enlist_fixture_connections
    @fixture_connections.each do |connection|
      connection.begin_transaction joinable: false
      connection.pool.lock_thread = true
    end

    # When connections are established in the future, begin a transaction too
    @connection_subscriber = ActiveSupport::Notifications.subscribe("!connection.active_record") do |_, _, _, _, payload|
      spec_name = payload[:spec_name] if payload.key?(:spec_name)

      if spec_name
        begin
          connection = ActiveRecord::Base.connection_handler.retrieve_connection(spec_name)
        rescue ConnectionNotEstablished
          connection = nil
        end

        if connection && !@fixture_connections.include?(connection)
          connection.begin_transaction joinable: false
          connection.pool.lock_thread = true
          @fixture_connections << connection
        end
      end
    end

  # Load fixtures for every test.
  else
    ActiveRecord::FixtureSet.reset_cache
    @@already_loaded_fixtures[self.class] = nil
    @loaded_fixtures = load_fixtures(config)
  end

  # Instantiate fixtures for every test if requested.
  instantiate_fixtures if use_instantiated_fixtures
end

# File activerecord/lib/active_record/fixtures.rb, line 1006
def teardown_fixtures
  # Rollback changes if a transaction is active.
  if run_in_transaction?
    ActiveSupport::Notifications.unsubscribe(@connection_subscriber) if @connection_subscriber
    @fixture_connections.each do |connection|
      connection.rollback_transaction if connection.transaction_open?
      connection.pool.lock_thread = false
    end
    @fixture_connections.clear
  else
    ActiveRecord::FixtureSet.reset_cache
  end

  ActiveRecord::Base.clear_active_connections!
end