code: def _test_cov(self, pdf):
      psdf = ps.from_pandas(pdf)
  
      self.assert_eq(
          pdf["s1"].cov(pdf["s2"]),
          psdf["s1"].cov(psdf["s2"]),
          almost=True,
      )
      self.assert_eq(
          pdf["s1"].cov(pdf["s2"], ddof=2),
          psdf["s1"].cov(psdf["s2"], ddof=2),
          almost=True,
      )
  
      self.assert_eq(
          pdf["s1"].cov(pdf["s2"], min_periods=3),
          psdf["s1"].cov(psdf["s2"], min_periods=3),
          almost=True,
      )
      self.assert_eq(
          pdf["s1"].cov(pdf["s2"], min_periods=3, ddof=-1),
          psdf["s1"].cov(psdf["s2"], min_periods=3, ddof=-1),
          almost=True,
      )
  
      self.assert_eq(
          pdf["s1"].cov(pdf["s2"], min_periods=4),
          psdf["s1"].cov(psdf["s2"], min_periods=4),
          almost=True,
      )
      self.assert_eq(
          pdf["s1"].cov(pdf["s2"], min_periods=4, ddof=3),
          psdf["s1"].cov(psdf["s2"], min_periods=4, ddof=3),
          almost=True,
      )
  
imports: import unittest
  from decimal import Decimal
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.testing.pandasutils import ComparisonTestBase
  from pyspark.testing.sqlutils import SQLTestUtils
label_desc: Use image node_id 23 for calling the SeriesStatMixin obj's underlying member method code with example usage: obj._test_cov(pdf) without return types