class_docstr: Unit tests for calibration.
class_docstr_tok: ["Unit","tests","for","calibration","."]
docstr: Create a mocked file handler.
docstr_tok: ["Create","a","mocked","file","handler","."]
code: def file_handler(self):
      """Create a mocked file handler."""
      header = {
          "15_DATA_HEADER": {
              "ImageAcquisition": {
                  "PlannedAcquisitionTime": {
                      "TrueRepeatCycleStart": self.scan_time
                  }
              }
          }
      }
      trailer = {
          "15TRAILER": {
              "ImageProductionStats": {
                  "ActualScanningSummary": {
                      "ForwardScanStart": self.scan_time
                  }
              }
          }
      }
      header["15_DATA_HEADER"].update(TEST_HEADER_CALIB)
      with mock.patch(
          "satpy.readers.seviri_l1b_native.NativeMSGFileHandler.__init__",
          return_value=None,
      ):
          fh = NativeMSGFileHandler(
              filename=None, filename_info={}, filetype_info=None
          )
          fh.header = header
          fh.trailer = trailer
          fh.platform_id = self.platform_id
          return fh
  
imports: from __future__ import annotations
  import os
  import unittest
  import warnings
  from datetime import datetime
  from unittest import mock
  import dask.array
  import numpy
  import pytest
  import xarray
  from satpy.readers.eum_base import recarray2dict, time_cds_short
  from satpy.readers.seviri_l1b_native import ASCII_STARTSWITH, ImageBoundaries, NativeMSGFileHandler, Padder, get_available_channels, has_archive_header
  from satpy.tests.reader_tests.test_seviri_base import ORBIT_POLYNOMIALS, ORBIT_POLYNOMIALS_INVALID
  from satpy.tests.reader_tests.test_seviri_l1b_calibration import TestFileHandlerCalibrationBase
  from satpy.tests.utils import assert_attrs_equal, make_dataid
label_desc: Use image node_id 1 for calling the TestNativeMSGCalibration obj's underlying member method code with example usage: obj.file_handler() and returns: fh