old_contents: 
  import unittest
  
  from vcp.system_package_manager_handlers import SystemPackageManagerHandlerFactory
  
  from voidpp_tools.mocks.file_system import mockfs
  
  OS_RELEASE = dict(
      ubuntu = u"""
  NAME="Ubuntu"
  VERSION="14.04.1 LTS, Trusty Tahr"
  ID=ubuntu
  ID_LIKE=debian
  PRETTY_NAME="Ubuntu 14.04.1 LTS"
  VERSION_ID="14.04"
  HOME_URL="http://www.ubuntu.com/"
  SUPPORT_URL="http://help.ubuntu.com/"
  BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
  """,
      debian = u"""
  PRETTY_NAME="Debian GNU/Linux 8 (jessie)"
  NAME="Debian GNU/Linux"
  VERSION_ID="8"
  VERSION="8 (jessie)"
  ID=debian
  HOME_URL="http://www.debian.org/"
  SUPPORT_URL="http://www.debian.org/support"
  BUG_REPORT_URL="https://bugs.debian.org/"
  """
  )
  
  class TestSystemPackageManagerHandler(unittest.TestCase):
  
      @mockfs(dict(etc = {'os-release': OS_RELEASE['debian']}))
      def test_get_current_ubuntu(self):
          # Arrange
          factory = SystemPackageManagerHandlerFactory()
  
          # Act
          os_type = factory.get_current()
  
          # Assert
          self.assertEqual(os_type, 'debian')
  
      @mockfs(dict(etc = {'os-release': OS_RELEASE['ubuntu']}))
      def test_get_current_ubuntu(self):
          # Arrange
          factory = SystemPackageManagerHandlerFactory()
  
          # Act
          os_type = factory.get_current()
  
          # Assert
          self.assertEqual(os_type, 'ubuntu')
  
new_contents: 
  import unittest
  
  from vcp.system_package_manager_handlers import SystemPackageManagerHandlerFactory
  
  from voidpp_tools.mocks.file_system import mockfs
  
  OS_RELEASE = dict(
      ubuntu = u"""
  NAME="Ubuntu"
  VERSION="14.04.1 LTS, Trusty Tahr"
  ID=ubuntu
  ID_LIKE=debian
  PRETTY_NAME="Ubuntu 14.04.1 LTS"
  VERSION_ID="14.04"
  HOME_URL="http://www.ubuntu.com/"
  SUPPORT_URL="http://help.ubuntu.com/"
  BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
  """,
      debian = u"""
  PRETTY_NAME="Debian GNU/Linux 8 (jessie)"
  NAME="Debian GNU/Linux"
  VERSION_ID="8"
  VERSION="8 (jessie)"
  ID=debian
  HOME_URL="http://www.debian.org/"
  SUPPORT_URL="http://www.debian.org/support"
  BUG_REPORT_URL="https://bugs.debian.org/"
  """
  )
  
  class TestSystemPackageManagerHandler(unittest.TestCase):
  
      @mockfs(dict(etc = {'os-release': OS_RELEASE['debian']}))
      def test_get_current_debian(self):
          # Arrange
          factory = SystemPackageManagerHandlerFactory()
  
          # Act
          os_type = factory.get_current()
  
          # Assert
          self.assertEqual(os_type, 'debian')
  
      @mockfs(dict(etc = {'os-release': OS_RELEASE['ubuntu']}))
      def test_get_current_ubuntu(self):
          # Arrange
          factory = SystemPackageManagerHandlerFactory()
  
          # Act
          os_type = factory.get_current()
  
          # Assert
          self.assertEqual(os_type, 'ubuntu')
  
      @mockfs()
      def test_get_current_missing_file(self):
          # Arrange
          factory = SystemPackageManagerHandlerFactory()
  
          # Act
          os_type = factory.get_current()
  
          # Assert
          self.assertIsNone(os_type)
  
subject: Add more tests