code: def test_invresz_one_coefficient_bug(self, xp, scp):
      # Regression test for issue in gh-4646.
      r = xp.asarray([1])
      p = xp.asarray([2])
      k = xp.asarray([0])
      b, a = scp.signal.invresz(r, p, k)
      return b, a
  
imports: import numpy
  import pytest
  import cupy
  from cupy import testing
  import cupyx.scipy.signal
label_desc: Use image node_id 13 for calling the TestPartialFractionExpansion obj's underlying member method code with example usage: obj.test_invresz_one_coefficient_bug(xp, scp) and returns: b,  a