docstr: check the transform of one impulse at a random place 
docstr_tok: ["check","the","transform","of","one","impulse","at","a","random","place"]
code: def test_impulse(self):
      """check the transform of one impulse at a random place"""
      win_s = 256
      i = int(floor(random() * win_s))
      impulse = pi * random()
      f = fft(win_s)
      timegrain = fvec(win_s)
      timegrain[i] = impulse
      fftgrain = f(timegrain)
      # self.plot_this ( fftgrain.phas )
      assert_almost_equal(fftgrain.norm, impulse, decimal=6)
      assert_equal(fftgrain.phas <= pi, True)
      assert_equal(fftgrain.phas >= -pi, True)
  
imports: from numpy.testing import TestCase
  from numpy.testing import assert_equal, assert_almost_equal
  import numpy
  from aubio import fvec, fft, cvec
  from math import pi, floor
  from random import random
label_desc: Use image node_id 4 for calling the aubio_fft_test_case obj's underlying member method code with example usage: obj.test_impulse() without return types