instance method setup_transactional_fixtures

# File activerecord/lib/active_record/test_fixtures.rb, line 192
      def setup_transactional_fixtures
        setup_shared_connection_pool

        # Begin transactions for connections already established
        pools = ActiveRecord::Base.connection_handler.connection_pool_list(:writing)

        # Filter to pools that want to use transactions
        pools.select! { |pool| transactional_tests_for_pool?(pool) }

        # Record each pool as it is pinned. Teardown raises for a pool it is
        # asked to unpin that never was, which buries whatever stopped it.
        pools.each do |pool|
          pool.pin_connection!(lock_threads)
          @fixture_connection_pools << pool
          pool.lease_connection
        end

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

          if connection_name
            pool = ActiveRecord::Base.connection_handler.retrieve_connection_pool(connection_name, shard: shard)
            if pool
              setup_shared_connection_pool

              # Don't begin a transaction if we've already done so, or are not using them for this pool
              if !@fixture_connection_pools.include?(pool) && transactional_tests_for_pool?(pool)
                pool.pin_connection!(lock_threads)
                @fixture_connection_pools << pool
                pool.lease_connection
              end
            end
          end
        end
      end