old_contents: 
  import os.path
  
  import numpy as np
  
  from eccodes_grib import xarray_store
  
  SAMPLE_DATA_FOLDER = os.path.join(os.path.dirname(__file__), 'sample-data')
  TEST_DATA = os.path.join(SAMPLE_DATA_FOLDER, 'era5-levels-members.grib')
  
  
  def test_all():
      da = xarray_store.open_dataset(TEST_DATA).data_vars['t']
  
      assert np.allclose(da.mean(), 262.92133)
  
new_contents: 
  import os.path
  
  import numpy as np
  
  from eccodes_grib import xarray_store
  
  SAMPLE_DATA_FOLDER = os.path.join(os.path.dirname(__file__), 'sample-data')
  TEST_DATA = os.path.join(SAMPLE_DATA_FOLDER, 'era5-levels-members.grib')
  
  
  def test_all():
      da = xarray_store.open_dataset(TEST_DATA).data_vars['t']
  
      assert np.allclose(da.mean(), 262.92133)
      assert np.allclose(da.sel(level=50000).mean(), 252.22284)
      assert np.allclose(da.sel(number=slice(2, 5)).mean(), 262.92184)
      assert np.allclose(da.sel(latitude=slice(90, 40), longitude=slice(0, 33)).mean(), 250.58322)
  
subject: Add some slice tests.