code: def test_expanding_indexer():
      s = Series(range(10))
      indexer = ExpandingIndexer()
      result = s.rolling(indexer).mean()
      expected = s.expanding().mean()
      tm.assert_series_equal(result, expected)
  
imports: import numpy
  import pytest
  from pandas import DataFrame, MultiIndex, Series, concat, date_range
  import pandas._testing
  from pandas.api.indexers import BaseIndexer, FixedForwardWindowIndexer
  from pandas.core.indexers.objects import ExpandingIndexer, FixedWindowIndexer, VariableOffsetWindowIndexer
  from pandas.tseries.offsets import BusinessDay
label_desc: Use image node_id 2 for calling a global function with example usage: test_expanding_indexer() without return types