docstr: check the transform of one impulse at a index 0 
docstr_tok: ["check","the","transform","of","one","impulse","at","a","index","0"]
code: def test_impulse_at_zero(self):
      """check the transform of one impulse at a index 0"""
      win_s = 1024
      impulse = pi
      f = fft(win_s)
      timegrain = fvec(win_s)
      timegrain[0] = impulse
      fftgrain = f(timegrain)
      # self.plot_this ( fftgrain.phas )
      assert_equal(fftgrain.phas[0], 0)
      # could be 0 or -0 depending on fft implementation (0 for fftw3, -0 for ooura)
      assert_almost_equal(fftgrain.phas[1], 0)
      assert_almost_equal(fftgrain.norm[0], impulse, decimal=6)
  
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 6 for calling the aubio_fft_test_case obj's underlying member method code with example usage: obj.test_impulse_at_zero() without return types