code: def test_mean(self):
      string_series = Series(range(20), dtype=np.float64, name="series")
      self._check_stat_op("mean", np.mean, string_series)
  
imports: import inspect
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Series, date_range
  import pandas._testing
label_desc: Use image node_id 3 for calling the TestSeriesStatReductions obj's underlying member method code with example usage: obj.test_mean() without return types