code: def test_mad_empty(self):
      empty = np.empty(0)
      assert np.isnan(scale.mad(empty))
      empty = np.empty((10, 100, 0))
      assert_equal(scale.mad(empty, axis=1), np.empty((10, 0)))
      empty = np.empty((100, 100, 0, 0))
      assert_equal(scale.mad(empty, axis=-1), np.empty((100, 100, 0)))
  
imports: import numpy
  from numpy.random import standard_normal
  from numpy.testing import assert_almost_equal, assert_equal
  import pytest
  from scipy.stats import norm
  import statsmodels.api
  import statsmodels.robust.scale
  from statsmodels.robust.scale import mad
label_desc: Use image node_id 3 for calling the TestMad obj's underlying member method code with example usage: obj.test_mad_empty() without return types