code: def sum_agg_func_fixture():
      """
      Register a unary aggregate function (mean)
      """
  
      def func(ctx, x, *args):
          return pa.scalar(np.nansum(x))
  
      func_name = "sum_udf"
      func_doc = empty_udf_doc
  
      pc.register_aggregate_function(
          func,
          func_name,
          func_doc,
          {
              "x": pa.float64(),
          },
          pa.float64(),
      )
      return func, func_name
  
imports: import pytest
  import numpy
  import pyarrow
  from pyarrow import compute
label_desc: Use image node_id 2 for calling a global function with example usage: sum_agg_func_fixture() and returns: func,  func_name, pa