old_contents: from setuptools.dist import Distribution
  from setuptools.command.build import build
  
  
  def test_distribution_gives_setuptools_build_obj(tmpdir_cwd):
      """
      Check that the setuptools Distribution uses the
      setuptools specific build object.
      """
      dist = Distribution(dict(
          script_name='setup.py',
          script_args=['build'],
          packages=[''],
          package_data={'': ['path/*']},
      ))
      assert isinstance(dist.get_command_obj("build"), build)
  
new_contents: from setuptools.dist import Distribution
  from setuptools.command.build import build
  from distutils.command.build import build as distutils_build
  
  
  def test_distribution_gives_setuptools_build_obj(tmpdir_cwd):
      """
      Check that the setuptools Distribution uses the
      setuptools specific build object.
      """
      dist = Distribution(dict(
          script_name='setup.py',
          script_args=['build'],
          packages=[''],
          package_data={'': ['path/*']},
      ))
  
      build_obj = dist.get_command_obj("build")
      assert isinstance(build_obj, build)
  
      build_obj.sub_commands.append(("custom_build_subcommand", None))
  
      distutils_subcommands = [cmd[0] for cmd in distutils_build.sub_commands]
      assert "custom_build_subcommand" not in distutils_subcommands
  
subject: Test that extending setuptools' build sub_commands does not extend distutils