code: def test_nunique(self):
      pser = pd.Series([1, 2, 1, np.nan])
      psser = ps.from_pandas(pser)
  
      # Assert NaNs are dropped by default
      nunique_result = psser.nunique()
      self.assertEqual(nunique_result, 2)
      self.assert_eq(nunique_result, pser.nunique())
  
      # Assert including NaN values
      nunique_result = psser.nunique(dropna=False)
      self.assertEqual(nunique_result, 3)
      self.assert_eq(nunique_result, pser.nunique(dropna=False))
  
      # Assert approximate counts
      self.assertEqual(ps.Series(range(100)).nunique(approx=True), 103)
      self.assertEqual(
          ps.Series(range(100)).nunique(approx=True, rsd=0.01), 100
      )
  
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 1 for calling the SeriesStatMixin obj's underlying member method code with example usage: obj.test_nunique() without return types