code: def test_contains_nan(self):
      ci = CategoricalIndex(
          list("aabbca") + [np.nan], categories=list("cabdef")
      )
      assert np.nan in ci
  
imports: import numpy
  import pytest
  from pandas.errors import InvalidIndexError
  import pandas
  from pandas import CategoricalIndex, Index, IntervalIndex, Timestamp
  import pandas._testing
label_desc: Use image node_id 2 for calling the TestContains obj's underlying member method code with example usage: obj.test_contains_nan() without return types