=False`` the comparison is skipped, since it does not
  make sense with ShortTimeFFT.istft(). Only used in test
  TestSTFT.test_roundtrip_boundary_extension().
* If ShortTimeFFT.istft() decides the STFT is not invertible, the
  comparison is skipped, since istft() only emits a warning and does not
  return a correct result. Only used in
  ShortTimeFFT.test_roundtrip_not_nola().
* For comparing the signals an absolute tolerance of the floating point
  resolution was added to account for the low accuracy of float32 (Occurs
  only in TestSTFT.test_roundtrip_float32()).
)