code: def test_fit_qt1():
      """Testing FitQt1 interface."""
      # Create a node object
      fit_qt1 = FitQt1()
  
      # Check if the command is properly defined
      cmd = get_custom_path("fit_qt1", env_dir="NIFTYFITDIR")
      assert fit_qt1.cmd == cmd
  
      # test raising error with mandatory args absent
      with pytest.raises(ValueError):
          fit_qt1.run()
  
      # Regular test:
      in_file = example_data("TI4D.nii.gz")
      fit_qt1.inputs.source_file = in_file
  
      cmd_tmp = "{cmd} -source {in_file} -comp {comp} -error {error} -m0map \
  {map0} -mcmap {cmap} -res {res} -syn {syn} -t1map {t1map}"
  
      expected_cmd = cmd_tmp.format(
          cmd=cmd,
          in_file=in_file,
          comp="TI4D_comp.nii.gz",
          map0="TI4D_m0map.nii.gz",
          error="TI4D_error.nii.gz",
          cmap="TI4D_mcmap.nii.gz",
          res="TI4D_res.nii.gz",
          t1map="TI4D_t1map.nii.gz",
          syn="TI4D_syn.nii.gz",
      )
  
      assert fit_qt1.cmdline == expected_cmd
  
      # Runs T1 fitting to inversion and saturation recovery data (NLSQR)
      fit_qt1_2 = FitQt1(tis=[1, 2, 5], ir_flag=True)
      in_file = example_data("TI4D.nii.gz")
      fit_qt1_2.inputs.source_file = in_file
  
      cmd_tmp = "{cmd} -source {in_file} -IR -TIs 1.0 2.0 5.0 \
  -comp {comp} -error {error} -m0map {map0} -mcmap {cmap} -res {res} \
  -syn {syn} -t1map {t1map}"
  
      expected_cmd = cmd_tmp.format(
          cmd=cmd,
          in_file=in_file,
          comp="TI4D_comp.nii.gz",
          map0="TI4D_m0map.nii.gz",
          error="TI4D_error.nii.gz",
          cmap="TI4D_mcmap.nii.gz",
          res="TI4D_res.nii.gz",
          t1map="TI4D_t1map.nii.gz",
          syn="TI4D_syn.nii.gz",
      )
  
      assert fit_qt1_2.cmdline == expected_cmd
  
      # Runs T1 fitting to spoiled gradient echo (SPGR) data (NLSQR)
      fit_qt1_3 = FitQt1(flips=[2, 4, 8], spgr=True)
      in_file = example_data("TI4D.nii.gz")
      fit_qt1_3.inputs.source_file = in_file
  
      cmd_tmp = "{cmd} -source {in_file} -comp {comp} -error {error} \
  -flips 2.0 4.0 8.0 -m0map {map0} -mcmap {cmap} -res {res} -SPGR -syn {syn} \
  -t1map {t1map}"
  
      expected_cmd = cmd_tmp.format(
          cmd=cmd,
          in_file=in_file,
          comp="TI4D_comp.nii.gz",
          map0="TI4D_m0map.nii.gz",
          error="TI4D_error.nii.gz",
          cmap="TI4D_mcmap.nii.gz",
          res="TI4D_res.nii.gz",
          t1map="TI4D_t1map.nii.gz",
          syn="TI4D_syn.nii.gz",
      )
  
      assert fit_qt1_3.cmdline == expected_cmd
  
imports: import pytest
  from ....testing import example_data
  from ...niftyreg import get_custom_path
  from ...niftyreg.tests.test_regutils import no_nifty_tool
  from ..qt1 import FitQt1
label_desc: Use image node_id 1 for calling a global function with example usage: test_fit_qt1() without return types