def test_make_subdirectory(self):
        """Test make_subdirectory increments generation."""
        self.assertEqual(self.volume.generation, 0)
        node = self.vgw.make_subdirectory(self.vgw.get_root().id, 'The Dir')
        self.assertEqual(node.generation, 1)
        self.assertEqual(self.volume.generation, 1)