class_docstr: Give access to files in the `models` directory.
code: def file(self, filename):
      return str(self._basedir / filename)
  
file_path: OMLT/tests/conftest.py
imports: from pathlib import Path
  import numpy
  import pytest
  from pyomo.common.fileutils import this_file_dir
  from omlt.neuralnet.layer import DenseLayer, InputLayer
  from omlt.neuralnet.network_definition import NetworkDefinition
label_desc: Use image node_id 2 for calling the _Datadir obj's underlying member method code with example usage: obj.file(filename) and returns: str