code: def diamond_sfn(data, msk, myrad, bcast_var):
      assert not np.any(msk[~Diamond(3).mask_])
      if np.all(msk[Diamond(3).mask_]):
          return 1.0
      return None
  
file_path: brainiak/tests/searchlight/test_searchlight.py
imports: from collections import namedtuple
  import numpy
  from mpi4py import MPI
  import conftest
  from brainiak.searchlight.searchlight import Searchlight
  from brainiak.searchlight.searchlight import Diamond, Ball
label_desc: Use image node_id 4 for calling a global function with example usage: diamond_sfn(data, msk, myrad, bcast_var) and returns: None, int