code: def get_fdata(self):
      return self.arr.astype(np.float64)
  
imports: import warnings
  from itertools import product
  import numpy
  import pytest
  from ..filebasedimages import FileBasedHeader, FileBasedImage, SerializableImage
  from .test_image_api import GenericImageAPI, SerializeMixin
label_desc: Use image node_id 5 for calling the FBNumpyImage obj's underlying member method code with example usage: obj.get_fdata() and returns: self