code: def test_zero_crossing_rate(self):
      a = np.array([0, 1, -1], dtype=float_type)
      assert_almost_equal(zero_crossing_rate(a), 1.0 / 3.0)
  
imports: import numpy
  from numpy.testing import TestCase, assert_equal, assert_almost_equal
  from aubio import fvec, zero_crossing_rate, alpha_norm, min_removal
  from aubio import float_type
label_desc: Use image node_id 1 for calling the aubio_zero_crossing_rate_test obj's underlying member method code with example usage: obj.test_zero_crossing_rate() without return types