old_contents: import os
  from build_pack_utils import BuildPack
  from common.integration import DirectoryHelper
  from common.integration import OptionsHelper
  
  
  class BaseCompileApp(object):
      def setUp(self):
          self.dh = DirectoryHelper()
          (self.build_dir,
           self.cache_dir,
           self.temp_dir) = self.dh.create_bp_env(self.app_name)
          self.bp = BuildPack({
              'BUILD_DIR': self.build_dir,
              'CACHE_DIR': self.cache_dir,
              'TMPDIR': self.temp_dir
          }, '.')
          if 'BP_DEBUG' in os.environ.keys():
              self.bp._ctx['BP_DEBUG'] = True
          self.dh.copy_build_pack_to(self.bp.bp_dir)
          self.dh.register_to_delete(self.bp.bp_dir)
          self.opts = OptionsHelper(os.path.join(self.bp.bp_dir,
                                                 'defaults',
                                                 'options.json'))
          self.opts.set_download_url(
              'http://localhost:5000/binaries/{STACK}')
  
          os.environ["CF_STACK"] = "cflinuxfs3"
  
      def tearDown(self):
          self.dh.cleanup()
  
          del os.environ["CF_STACK"]
  
new_contents: import os
  from build_pack_utils import BuildPack
  from common.integration import DirectoryHelper
  from common.integration import OptionsHelper
  
  
  class BaseCompileApp(object):
      def setUp(self):
          self.dh = DirectoryHelper()
          (self.build_dir,
           self.cache_dir,
           self.temp_dir) = self.dh.create_bp_env(self.app_name)
          self.bp = BuildPack({
              'BUILD_DIR': self.build_dir,
              'CACHE_DIR': self.cache_dir,
              'TMPDIR': self.temp_dir
          }, '.')
          if 'BP_DEBUG' in os.environ.keys():
              self.bp._ctx['BP_DEBUG'] = True
          self.dh.copy_build_pack_to(self.bp.bp_dir)
          self.dh.register_to_delete(self.bp.bp_dir)
          self.opts = OptionsHelper(os.path.join(self.bp.bp_dir,
                                                 'defaults',
                                                 'options.json'))
          self.opts.set_download_url(
              'http://localhost:5000/binaries/{STACK}')
  
          os.environ["CF_STACK"] = "cflinuxfs2"
  
      def tearDown(self):
          self.dh.cleanup()
  
          del os.environ["CF_STACK"]
  
subject: Revert "Bump the stack from cflinuxfs2 to cflinuxfs3 for python tests which run in the ci image, which appears to be an Ubuntu Bionic based image."