code: def testBadBroadcast(self, dtype, unit):
      test_string = [
          [b"ten", b"eleven", b"twelve"],
          [b"thirteen", b"fourteen", b"fifteen"],
          [b"sixteen", b"seventeen", b"eighteen"],
      ]
      position = np.array([1, 2, -3, 4], dtype)
      length = np.array([1, 2, 3, 4], dtype)
      with self.assertRaises(ValueError):
          string_ops.substr(test_string, position, length, unit=unit)
  
imports: from absl.testing import parameterized
  import numpy
  from tensorflow.python.framework import errors_impl
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import string_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 7 for calling the SubstrOpTest obj's underlying member method code with example usage: obj.testBadBroadcast(dtype, unit) without return types