old_contents: import os
  import tempfile
  import shutil
  
  from unittest import TestCase
  import yaml
  
  from dusty import constants
  from dusty.runner.compose import _write_composefile
  
  class TestComposeRunner(TestCase):
      def setUp(self):
          self.temp_compose_dir = tempfile.mkdtemp()
          self.temp_compose_path = os.path.join(self.temp_compose_dir, 'docker-compose.yml')
          self.old_compose_dir = constants.COMPOSE_DIR
          constants.COMPOSE_DIR = self.temp_compose_dir
          self.test_spec = {'app-a': {'image': 'app/a'}}
  
      def tearDown(self):
          constants.COMPOSE_DIR = self.old_compose_dir
          shutil.rmtree(self.temp_compose_dir)
  
      def test_write_composefile(self):
          _write_composefile(self.test_spec)
          written = open(self.temp_compose_path, 'r').read()
          self.assertItemsEqual(yaml.load(written), self.test_spec)
  
new_contents: import os
  import tempfile
  import shutil
  
  from unittest import TestCase
  from mock import patch
  import yaml
  
  from dusty import constants
  from dusty.runner.compose import _write_composefile, _get_docker_env
  
  class TestComposeRunner(TestCase):
      def setUp(self):
          self.temp_compose_dir = tempfile.mkdtemp()
          self.temp_compose_path = os.path.join(self.temp_compose_dir, 'docker-compose.yml')
          self.old_compose_dir = constants.COMPOSE_DIR
          constants.COMPOSE_DIR = self.temp_compose_dir
          self.test_spec = {'app-a': {'image': 'app/a'}}
  
      def tearDown(self):
          constants.COMPOSE_DIR = self.old_compose_dir
          shutil.rmtree(self.temp_compose_dir)
  
      def test_write_composefile(self):
          _write_composefile(self.test_spec)
          written = open(self.temp_compose_path, 'r').read()
          self.assertItemsEqual(yaml.load(written), self.test_spec)
  
      @patch('dusty.runner.compose._check_output_demoted')
      def test_get_docker_env(self, fake_check_output):
          fake_check_output.return_value = """    export DOCKER_TLS_VERIFY=1
          export DOCKER_HOST=tcp://192.168.59.103:2376
          export DOCKER_CERT_PATH=/Users/root/.boot2docker/certs/boot2docker-vm"""
          expected = {'DOCKER_TLS_VERIFY': '1',
                      'DOCKER_HOST': 'tcp://192.168.59.103:2376',
                      'DOCKER_CERT_PATH': '/Users/root/.boot2docker/certs/boot2docker-vm'}
          result = _get_docker_env()
          self.assertItemsEqual(result, expected)
  
subject: Add a test for _get_docker_env