code: def test_empty(self):
      # Regression test for gh-2832.
      # When there are no relative extrema, make sure that
      # the number of empty arrays returned matches the
      # dimension of the input.
  
      empty_array = np.array([], dtype=int)
  
      z1 = np.zeros(5)
  
      i = argrelmin(z1)
      assert_equal(len(i), 1)
      assert_array_equal(i[0], empty_array)
  
      z2 = np.zeros((3, 5))
  
      row, col = argrelmin(z2, axis=0)
      assert_array_equal(row, empty_array)
      assert_array_equal(col, empty_array)
  
      row, col = argrelmin(z2, axis=1)
      assert_array_equal(row, empty_array)
      assert_array_equal(col, empty_array)
  
imports: import copy
  import numpy
  from numpy.testing import assert_, assert_equal, assert_allclose, assert_array_equal
  import pytest
  from pytest import raises, warns
  from scipy.signal._peak_finding import argrelmax, argrelmin, peak_prominences, peak_widths, _unpack_condition_args, find_peaks, find_peaks_cwt, _identify_ridge_lines
  from scipy.signal._peak_finding_utils import _local_maxima_1d, PeakPropertyWarning
label_desc: Use image node_id 1 for calling the TestArgrel obj's underlying member method code with example usage: obj.test_empty() without return types