class_docstr: Test SEVIRI base.
docstr: Get scan start timestamp for testing.
docstr_tok: ["Get","scan","start","timestamp","for","testing","."]
code: def observation_start_time(self):
      """Get scan start timestamp for testing."""
      return datetime(2023, 3, 20, 15, 0, 10, 691000)
  
imports: import unittest
  from datetime import datetime, timedelta
  import dask.array
  import numpy
  import pytest
  import xarray
  from satpy.readers.seviri_base import MEIRINK_COEFS, MEIRINK_EPOCH, NoValidOrbitParams, OrbitPolynomial, OrbitPolynomialFinder, SEVIRICalibrationHandler, chebyshev, dec10216, get_cds_time, get_padding_area, get_satpos, pad_data_horizontally, pad_data_vertically, round_nom_time
  from satpy.utils import get_legacy_chunk_size
label_desc: Use image node_id 8 for calling the SeviriBaseTest obj's underlying member method code with example usage: obj.observation_start_time() and returns: datetime