code: def get_fake_mda(nlines, ncols, start_time):
      """Create fake metadata."""
      nbits = 10
      tline = get_acq_time_cds(start_time, nlines)
      return {
          "number_of_bits_per_pixel": nbits,
          "number_of_lines": nlines,
          "number_of_columns": ncols,
          "data_field_length": nlines * ncols * nbits,
          "cfac": 5,
          "lfac": 5,
          "coff": 10,
          "loff": 10,
          "image_segment_line_quality": {
              "line_mean_acquisition": tline,
              "line_validity": np.full(nlines, 3),
              "line_radiometric_quality": np.full(nlines, 4),
              "line_geometric_quality": np.full(nlines, 4),
          },
      }
  
file_path: satpy/satpy/tests/reader_tests/test_seviri_l1b_hrit_setup.py
imports: from datetime import datetime
  from unittest import mock
  import numpy
  from satpy.readers.seviri_l1b_hrit import HRITMSGFileHandler, HRITMSGPrologueFileHandler
  from satpy.tests.reader_tests.test_seviri_base import ORBIT_POLYNOMIALS
label_desc: Use image node_id 6 for calling a global function with example usage: get_fake_mda(nlines, ncols, start_time) and returns: dict