code: def test_singleton(self, len_h, len_x):
      # gh-9844: lengths producing expected outputs
      h = np.zeros(len_h)
      h[len_h // 2] = 1.0  # make h a delta
      x = np.ones(len_x)
      y = upfirdn(h, x, 1, 1)
      want = np.pad(x, (len_h // 2, (len_h - 1) // 2), "constant")
      assert_allclose(y, want)
  
imports: import numpy
  from itertools import product
  from numpy.testing import assert_equal, assert_allclose
  from pytest import raises
  import pytest
  from scipy.signal import upfirdn, firwin
  from scipy.signal._upfirdn import _output_len, _upfirdn_modes
  from scipy.signal._upfirdn_apply import _pad_test
label_desc: Use image node_id 2 for calling the TestUpfirdn obj's underlying member method code with example usage: obj.test_singleton(len_h, len_x) without return types