code: def test_pure_function():
      from deepchem.utils.differentiation_utils import PureFunction
  
      class WrapperFunction(PureFunction):
          def _get_all_obj_params_init(self):
              return []
  
          def _set_all_obj_params(self, objparams):
              pass
  
      def fcn(x, y):
          return x + y
  
      pfunc = WrapperFunction(fcn)
      assert pfunc(1, 2) == 3
  
imports: import pytest
label_desc: Use image node_id 30 for calling a global function with example usage: test_pure_function() and returns: unknown, list