code: def test_string(self) -> None:
      a = np.array(["Amy", "Billy", "Cindy", "David"]).astype(object)
      tensor_def = numpy_helper.from_array(a, "test")
      self.assertEqual(tensor_def.name, "test")
      a_recover = numpy_helper.to_array(tensor_def)
      np.testing.assert_equal(a, a_recover)
  
imports: import unittest
  from typing import Any
  import numpy
  import parameterized
  import onnx
  from onnx import helper, numpy_helper
label_desc: Use image node_id 10 for calling the TestNumpyHelper obj's underlying member method code with example usage: obj.test_string() without return types