class_docstr: Test the get_dataset method.
docstr: Mock reader and file handler.
code: def _create_file_handler(reader):
      """Mock reader and file handler."""
      fh = _get_fh_mocked(
          reader=reader,
          chn_dict={"1": 0, "5": 0},
          start_line=None,
          end_line=None,
          strip_invalid_coords=False,
          filename_info={"orbit_number": 123},
          sensor="sensor",
      )
      return fh
  
imports: from datetime import datetime
  from unittest import TestCase, mock
  import dask.array
  import numpy
  import pytest
  import xarray
label_desc: Use image node_id 4 for calling the TestGetDataset obj's underlying member method code with example usage: obj._create_file_handler(reader) and returns: fh