code: def test_at_least_one_grouping_variable_required(df):
      with pytest.raises(
          ValueError, match="No grouping variables are present"
      ):
          GroupBy(["z"]).agg(df, x="mean")
  
file_path: seaborn/tests/_core/test_groupby.py
imports: import numpy
  import pandas
  import pytest
  from numpy.testing import assert_array_equal
  from seaborn._core.groupby import GroupBy
label_desc: Use image node_id 5 for calling a global function with example usage: test_at_least_one_grouping_variable_required(df) without return types