code: def get_model(self):
      class Model(chainer.Chain):
          def __init__(self, ops):
              super(Model, self).__init__()
              self.ops = ops
  
          def __call__(self, a, b):
              return eval(self.ops)
  
      return Model(self.ops)
  
imports: import chainer
  import chainer.functions
  from chainer import testing
  from chainer.testing import attr
  import numpy
  import pytest
  from onnx_chainer.testing import input_generator
  from onnx_chainer_tests.helper import ONNXModelTest
label_desc: Use image node_id 1 for calling the TestBinaryMathOperators obj's underlying member method code with example usage: obj.get_model() and returns: Model, eval