code: def test_rolling_cov(series):
      A = series
      B = A + np.random.default_rng(2).standard_normal(len(A))
  
      result = A.rolling(window=50, min_periods=25).cov(B)
      tm.assert_almost_equal(
          result.iloc[-1], np.cov(A[-50:], B[-50:])[0, 1]
      )
  
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 4 for calling a global function with example usage: test_rolling_cov(series) without return types