code: def test_fit_asl():
      """Testing FitAsl interface."""
      # Create the test node
      fit_asl = FitAsl()
  
      # Check if the command is properly defined
      cmd = get_custom_path("fit_asl", env_dir="NIFTYFIT_DIR")
      assert fit_asl.cmd == cmd
  
      # test raising error with mandatory args absent
      with pytest.raises(ValueError):
          fit_asl.run()
  
      # Tests on the interface:
      # Runs cbf fitting assuming all tissue is GM!
      in_file = example_data("asl.nii.gz")
      fit_asl.inputs.source_file = in_file
  
      cmd_tmp = (
          "{cmd} -source {in_file} -cbf {cbf} -error {error} -syn {syn}"
      )
      expected_cmd = cmd_tmp.format(
          cmd=cmd,
          in_file=in_file,
          cbf="asl_cbf.nii.gz",
          error="asl_error.nii.gz",
          syn="asl_syn.nii.gz",
      )
  
      assert fit_asl.cmdline == expected_cmd
  
      # Runs cbf fitting using IR/SR T1 data to estimate the local T1 and uses
      # the segmentation data to fit tissue specific blood flow parameters
      # (lambda,transit times,T1)
      fit_asl2 = FitAsl(sig=True)
      in_file = example_data("asl.nii.gz")
      t1map = example_data("T1map.nii.gz")
      seg = example_data("segmentation0.nii.gz")
      fit_asl2.inputs.source_file = in_file
      fit_asl2.inputs.t1map = t1map
      fit_asl2.inputs.seg = seg
  
      cmd_tmp = "{cmd} -source {in_file} -cbf {cbf} -error {error} \
  -seg {seg} -sig -syn {syn} -t1map {t1map}"
  
      expected_cmd = cmd_tmp.format(
          cmd=cmd,
          in_file=in_file,
          t1map=t1map,
          seg=seg,
          cbf="asl_cbf.nii.gz",
          error="asl_error.nii.gz",
          syn="asl_syn.nii.gz",
      )
  
      assert fit_asl2.cmdline == expected_cmd
  
imports: import pytest
  from ....testing import example_data
  from ...niftyreg import get_custom_path
  from ..asl import FitAsl
  from ...niftyreg.tests.test_regutils import no_nifty_tool
label_desc: Use image node_id 1 for calling a global function with example usage: test_fit_asl() without return types