code: def test_rolling_corr_bias_correction():
      # test for correct bias correction
      a = Series(
          np.arange(20, dtype=np.float64),
          index=date_range("2020-01-01", periods=20),
      )
      b = a.copy()
      a[:5] = np.nan
      b[:10] = np.nan
  
      result = a.rolling(window=len(a), min_periods=1).corr(b)
      tm.assert_almost_equal(result.iloc[-1], a.corr(b))
  
imports: import numpy
  import pytest
  from pandas.compat import IS64
  from pandas import DataFrame, Index, MultiIndex, Series, date_range
  import pandas._testing
  from pandas.core.algorithms import safe_sort
label_desc: Use image node_id 6 for calling a global function with example usage: test_rolling_corr_bias_correction() without return types