old_contents: import unittest
  from lib import create_master, Master
  
  class TestFactory(unittest.TestCase):
  
      def test_can_create_master(self):
          master = create_master("ipc:///tmp/worker", "ipc:///tmp/frontend")
          self.assertIsInstance(master, Master)
  
new_contents: import unittest
  from lib import create_master, Master
  
  class TestFactory(unittest.TestCase):
  
      def test_can_create_master(self):
          master = create_master("ipc:///tmp/worker", "ipc:///tmp/frontend", "ipc:///tmp/monitor/")
          self.assertIsInstance(master, Master)
  
subject: Test fixed.