code: def test_reg_f3d():
      """tests for reg_f3d interface"""
      # Create a reg_f3d object
      nr_f3d = RegF3D()
  
      # Check if the command is properly defined
      assert nr_f3d.cmd == get_custom_path("reg_f3d")
  
      # test raising error with mandatory args absent
      with pytest.raises(ValueError):
          nr_f3d.run()
  
      # Assign some input data
      ref_file = example_data("im1.nii")
      flo_file = example_data("im2.nii")
      rmask_file = example_data("mask.nii")
      nr_f3d.inputs.ref_file = ref_file
      nr_f3d.inputs.flo_file = flo_file
      nr_f3d.inputs.rmask_file = rmask_file
      nr_f3d.inputs.omp_core_val = 4
      nr_f3d.inputs.vel_flag = True
      nr_f3d.inputs.be_val = 0.1
      nr_f3d.inputs.le_val = 0.1
  
      cmd_tmp = "{cmd} -be 0.100000 -cpp {cpp} -flo {flo} -le 0.100000 -omp 4 \
  -ref {ref} -res {res} -rmask {rmask} -vel"
  
      expected_cmd = cmd_tmp.format(
          cmd=get_custom_path("reg_f3d"),
          cpp="im2_cpp.nii.gz",
          flo=flo_file,
          ref=ref_file,
          res="im2_res.nii.gz",
          rmask=rmask_file,
      )
  
      assert nr_f3d.cmdline == expected_cmd
  
imports: import pytest
  from ....testing import example_data
  from ..None import get_custom_path, RegAladin, RegF3D
  from .test_regutils import no_nifty_tool
label_desc: Use image node_id 2 for calling a global function with example usage: test_reg_f3d() without return types