new_contents: #!/usr/bin/env python
  
  from __future__ import print_function
  
  import unittest
  
  try:
      from unittest import mock
  except ImportError:
      import mock
  
  import imp
  import os.path
  
  
  import engines
  
  
  class TestInit(unittest.TestCase):
  
      def test_init(self):
          mock_engines = {}
  
          mock_listdir = mock.Mock(return_value=(
                  'text_engine.txt',
                  '0_engine.py',
                  '.period_engine.py',
                  '@at_engine.py',
                  '__init__.py',
                  '_underscore_engine.py',
                  'normal_engine.py',
                  'compiled_engine.pyc',
                  'optimized_engine.pyo',
              ))
  
          valid_engines = {
                  '_underscore_engine':   ('UnderscoreEngine', 'underscore'),
                  'normal_engine':        ('NormalEngine',     'normal'),
                  'compiled_engine':      ('CompiledEngine',   'compiled'),
                  'optimized_engine':     ('OptimizedEngine',  'optimized'),
              }
  
          result_dict = {handle: None for __, (__, handle) in valid_engines.items()}
  
          def mock_import_module(name, package):
              self.assertEqual(package, 'engines')
  
              assert name.startswith('.')
              name = name[1:]
  
              module = imp.new_module('%s.%s' % (package, name))
  
              if name == '__init__':
                  module.Engine = engines.Engine
              else:
                  self.assertIn(name, valid_engines)
                  class_name, engine_handle = valid_engines[name]
  
                  class MockEngine(engines.Engine):
                      handle = engine_handle
  
                  MockEngine.__name__ = class_name
                  MockEngine.__qualname__ = class_name
  
                  result_dict[engine_handle] = MockEngine
                  setattr(module, class_name, MockEngine)
  
              return module
  
          with mock.patch.object(engines, 'engines', mock_engines), \
               mock.patch('os.listdir', mock_listdir), \
               mock.patch('importlib.import_module', mock_import_module):
              engines._init()
  
          mock_listdir.assert_called_once_with(os.path.dirname(engines.__file__))
          self.assertDictEqual(mock_engines, result_dict)
  
  
  class TestEngine(unittest.TestCase):
  
      def test_not_instantiable(self):
          self.assertRaises(AssertionError, engines.Engine, dirname='/tmp/', tolerant=False)
  
      def test_handle_is_none(self):
          class TestEngine(engines.Engine):
              pass
  
          engine = TestEngine(dirname='/tmp/', tolerant=False)
  
          self.assertIsNone(engine.handle)
  
      def test_apply_not_implemented(self):
          class TestEngine(engines.Engine):
              pass
  
          engine = TestEngine(dirname='/tmp/', tolerant=False)
  
          self.assertRaises(NotImplementedError, engine.apply, {})
  
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Add tests for engines package.