code: def check_data(self):
          
          assert os.path.exists(self.data_fp)
          if gis:
              with fiona.drivers():
                  with fiona.open(self.faces_fp) as src:
                      assert src.meta
  
          gpkg_hash = json.load(open(self.data_fp))['metadata']['sha256']
          assert gpkg_hash == sha256(self.faces_fp)
docs: Check that definitions file is present, and that faces file is readable.