code: def test_fft_shift():
      freqs = fftfreq(9, d=1.0 / 9).reshape(3, 3)
      t = ifftshift(fftshift(freqs))
  
      assert t.dtype is not None
      expect_dtype = np.fft.ifftshift(
          np.fft.fftshift(np.fft.fftfreq(9, d=1.0 / 9).reshape(3, 3))
      ).dtype
      assert t.dtype == expect_dtype
  
file_path: mars/mars/tensor/fft/tests/test_fft.py
imports: import numpy
  from ....core import tile
  from ...datasource import ones
  from ..None import fft, ifft, fft2, ifft2, fftn, ifftn, rfft, irfft, rfft2, irfft2, rfftn, irfftn, hfft, ihfft, fftfreq, rfftfreq, fftshift, ifftshift
label_desc: Use image node_id 4 for calling a global function with example usage: test_fft_shift() without return types