code: def reference_fftn(self, a, axes):
      # numpy.fft.fftn doesn't support complex256 type,
      # so we need to compare to a lower precision type.
      a = numpy.complex128(a)
      return np_fft.fftn(a, axes=axes)
  
imports: from pyfftw import FFTW, byte_align, empty_aligned, forget_wisdom
  import pyfftw
  import numpy
  from timeit import Timer
  import time
  import unittest
  from .test_pyfftw_base import FFTWBaseTest, run_test_suites, miss, np_fft
label_desc: Use image node_id 2 for calling the ComplexLongDoubleFFTWTest obj's underlying member method code with example usage: obj.reference_fftn(a, axes) and returns: np_fft