code: def test_groupby_expanding_mean(self):
      self._test_groupby_expanding_func("mean")
  
file_path: spark/python/pyspark/pandas/tests/window/test_groupby_expanding.py
imports: import numpy
  import pandas
  import pyspark.pandas
  from pyspark.testing.pandasutils import PandasOnSparkTestCase, TestUtils
label_desc: Use image node_id 4 for calling the GroupByExpandingMixin obj's underlying member method code with example usage: obj.test_groupby_expanding_mean() without return types