code: def test_types(self):
      result = fft_frequencies(5, 10)
      self.assertIsInstance(result, np.ndarray)
      self.assertEqual(result.dtype, float)
  
imports: from __future__ import absolute_import, division, print_function
  import sys
  import unittest
  from os.path import join
  from madmom.audio.spectrogram import Spectrogram
  from madmom.audio.stft import *
  from .None import AUDIO_PATH
label_desc: Use image node_id 2 for calling the TestBinFrequenciesFunction obj's underlying member method code with example usage: obj.test_types() without return types