docstr: Tests that NetDefs can be added to MetaNetDefs
docstr_tok: ["Tests","that","NetDefs","can","be","added","to","MetaNetDefs"]
code: def test_adding_net(self):
      """
      Tests that NetDefs can be added to MetaNetDefs
      """
      meta_net_def = metanet_pb2.MetaNetDef()
      net_def = caffe2_pb2.NetDef()
      meta_net_def.nets.add(key="test_key", value=net_def)
  
imports: import tempfile
  import unittest
  import numpy
  from caffe2.python import cnn, workspace, core
  from caffe2.python.predictor_constants import predictor_constants
  import caffe2.python.predictor.predictor_exporter
  import caffe2.python.predictor.predictor_py_utils
  from caffe2.proto import caffe2_pb2, metanet_pb2
label_desc: Use image node_id 2 for calling the MetaNetDefTest obj's underlying member method code with example usage: obj.test_adding_net() without return types