def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def test_attach_detach_volume_to_instance(self):
        """Test attaching and detaching volume to instance"""
        # Create a server
        server = self.create_server()
        # Volume is attached and detached successfully from an instance
        self.volumes_client.attach_volume(self.volume['id'],
                                          instance_uuid=server['id'],
                                          mountpoint='/dev/%s' %
                                          CONF.compute.volume_device_name)
        waiters.wait_for_volume_resource_status(self.volumes_client,
                                                self.volume['id'], 'in-use')
        self.volumes_client.detach_volume(self.volume['id'])
        waiters.wait_for_volume_resource_status(self.volumes_client,
                                                self.volume['id'], 'available')