code: def test_rolloff(self):
      o = specdesc("rolloff")
      c = cvec()
      assert_equal(0.0, o(c))
      a = arange(c.length * 2, 0, -2, dtype=float_type)
      c.norm = a
      cumsum = 0.95 * sum(a * a)
      i = 0
      rollsum = 0
      while rollsum < cumsum:
          rollsum += a[i] * a[i]
          i += 1
      rolloff = i
      assert_equal(rolloff, o(c))
  
imports: from numpy.testing import TestCase, assert_equal, assert_almost_equal
  from numpy import random, arange, log, zeros
  from aubio import specdesc, cvec, float_type
label_desc: Use image node_id 15 for calling the aubio_specdesc obj's underlying member method code with example usage: obj.test_rolloff() without return types