code: def test_xarray_sel_iter_ordering_combined(
      sample_dataset,
  ):  # pylint: disable=invalid-name
      """Assert that varname order stays consistent when chains are combined"""
      _, _, data = sample_dataset
      var_names = [
          var
          for (var, _, _) in xarray_sel_iter(
              data, var_names=None, combined=True
          )
      ]
      assert set(var_names) == {"mu", "tau"}
  
imports: import importlib
  import numpy
  import pytest
  import xarray
  from ...data import from_dict
  from ...plots.backends.matplotlib import dealiase_sel_kwargs, matplotlib_kwarg_dealiaser
  from ...plots.plot_utils import compute_ranks, filter_plotters_list, format_sig_figs, get_plotting_function, make_2d, set_bokeh_circular_ticks_labels, vectorized_to_hex
  from ...rcparams import rc_context
  from ...sel_utils import xarray_sel_iter, xarray_to_ndarray
  from ...stats.density_utils import get_bins
  from ...utils import get_coords
  from ..helpers import running_on_ci
label_desc: Use image node_id 8 for calling a global function with example usage: test_xarray_sel_iter_ordering_combined(sample_dataset) without return types