code: def testNegativeDofFails(self):
      with self.assertRaisesOpError(r"Condition x > 0 did not hold"):
          student = student_t.StudentT(
              df=[2, -5.0],
              loc=0.0,
              scale=1.0,
              validate_args=True,
              name="S",
          )
          self.evaluate(student.mean())
  
imports: import importlib
  import math
  import numpy
  from tensorflow.python.eager import backprop
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import random_seed
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import nn_ops
  from tensorflow.python.ops.distributions import student_t
  from tensorflow.python.platform import test
  from tensorflow.python.platform import tf_logging
label_desc: Use image node_id 24 for calling the StudentTTest obj's underlying member method code with example usage: obj.testNegativeDofFails() without return types