code: def test_join_nestediters(tmpdir):
      tmpdir.chdir()
  
      def exponent(x, p):
          return x**p
  
      wf = pe.Workflow("wf", base_dir=tmpdir.strpath)
  
      xs = pe.Node(
          IdentityInterface(["x"]), iterables=[("x", [1, 2])], name="xs"
      )
      ps = pe.Node(
          IdentityInterface(["p"]), iterables=[("p", [3, 4])], name="ps"
      )
      exp = pe.Node(Function(function=exponent), name="exp")
      exp_joinx = pe.JoinNode(
          Merge(1, ravel_inputs=True),
          name="exp_joinx",
          joinsource="xs",
          joinfield=["in1"],
      )
      exp_joinp = pe.JoinNode(
          Merge(1, ravel_inputs=True),
          name="exp_joinp",
          joinsource="ps",
          joinfield=["in1"],
      )
      wf.connect(
          [
              (xs, exp, [("x", "x")]),
              (ps, exp, [("p", "p")]),
              (exp, exp_joinx, [("out", "in1")]),
              (exp_joinx, exp_joinp, [("out", "in1")]),
          ]
      )
  
      wf.run()
  
imports: import pytest
  from ....None import config
  from ...None import engine
  from ....interfaces import base
  from ....interfaces.utility import IdentityInterface, Function, Merge
  from ....interfaces.base import traits, File
label_desc: Use image node_id 14 for calling a global function with example usage: test_join_nestediters(tmpdir) and returns: unknown