docstr: Verify that psi exists and is the same as digamma
code: def test_psi(self):
      """Verify that psi exists and is the same as digamma"""
      assert cupyx.scipy.special.psi is cupyx.scipy.special.digamma
  
file_path: cupy/tests/cupyx_tests/scipy_tests/special_tests/test_digamma.py
imports: import unittest
  from cupy import testing
  import cupyx.scipy.special
  import numpy
label_desc: Use image node_id 6 for calling the TestDigamma obj's underlying member method code with example usage: obj.test_psi() without return types