code: def sgli_vn_file(tmp_path_factory):
      """Create a stub VN file."""
      filename = tmp_path_factory.mktemp("data") / "test_vn_file.h5"
      with h5py.File(filename, "w") as h5f:
          global_attributes = h5f.create_group("Global_attributes")
          global_attributes.attrs["Scene_start_time"] = np.array(
              [START_TIME.strftime("%Y%m%d %H:%M:%S.%f")[:-3]],
              dtype="|S21",
          )
          global_attributes.attrs["Scene_end_time"] = np.array(
              [END_TIME.strftime("%Y%m%d %H:%M:%S.%f")[:-3]],
              dtype="|S21",
          )
  
          image_data = h5f.create_group("Image_data")
          image_data.attrs["Number_of_lines"] = 1955
          image_data.attrs["Number_of_pixels"] = 1250
  
          vn01 = image_data.create_dataset(
              "Lt_VN01", data=FULL_KM_ARRAY, chunks=(116, 157)
          )
          vn01.attrs["Slope_reflectance"] = np.array(
              [5e-05], dtype=np.float32
          )
          vn01.attrs["Offset_reflectance"] = np.array(
              [-0.05], dtype=np.float32
          )
          vn01.attrs["Slope"] = np.array([0.02], dtype=np.float32)
          vn01.attrs["Offset"] = np.array([-25], dtype=np.float32)
          vn01.attrs["Mask"] = np.array([16383], dtype=np.uint16)
          vn01.attrs["Bit00(LSB)-13"] = np.array(
              [
                  b"Digital Number\n16383 : Missing value\n16382 : Saturation value"
              ],
              dtype="|S61",
          )
  
          add_downsampled_geometry_data(h5f)
  
      return filename
  
imports: import sys
  from datetime import datetime, timedelta
  import dask
  import h5py
  import numpy
  import pytest
  from satpy.readers.sgli_l1b import HDF5SGLI
label_desc: Use image node_id 1 for calling a global function with example usage: sgli_vn_file(tmp_path_factory) and returns: filename