class_docstr: Test the FY3E MERSI-LL L1B reader.
docstr: Test loading data when only 250m resolutions are available.
docstr_tok: ["Test","loading","data","when","only","250m","resolutions","are","available","."]
code: def test_250_resolutions(self):
      """Test loading data when only 250m resolutions are available."""
      from satpy.dataset.data_dict import get_key
      from satpy.readers import load_reader
      from satpy.tests.utils import make_dataid
  
      filenames = self.filenames_250m
      reader = load_reader(self.reader_configs)
      files = reader.select_files_from_pathnames(filenames)
      assert 2 == len(files)
      reader.create_filehandlers(files)
      # Make sure we have some files
      assert reader.file_handlers
  
      # Verify that we have multiple resolutions for:
      #     - Bands 6-7
      available_datasets = reader.available_dataset_ids
      for band_name in ("6", "7"):
          num_results = 2
          ds_id = make_dataid(name=band_name, resolution=250)
          res = get_key(
              ds_id,
              available_datasets,
              num_results=num_results,
              best=False,
          )
          assert num_results == len(res)
          ds_id = make_dataid(name=band_name, resolution=1000)
          with pytest.raises(KeyError):
              get_key(
                  ds_id,
                  available_datasets,
                  num_results=num_results,
                  best=False,
              )
  
      res = reader.load(["1", "6", "7"])
      assert 2 == len(res)
      with pytest.raises(KeyError):
          res.__getitem__("1")
      assert (2 * 40, 2048 * 2) == res["6"].shape
      assert "brightness_temperature" == res["6"].attrs["calibration"]
      assert "K" == res["6"].attrs["units"]
      assert (2 * 40, 2048 * 2) == res["7"].shape
      assert "brightness_temperature" == res["7"].attrs["calibration"]
      assert "K" == res["7"].attrs["units"]
  
imports: import os
  from unittest import mock
  import dask.array
  import numpy
  import pytest
  import xarray
  from satpy.tests.reader_tests.test_hdf5_utils import FakeHDF5FileHandler
label_desc: Use image node_id 4 for calling the TestMERSILLL1B obj's underlying member method code with example usage: obj.test_250_resolutions() without return types