code: def test_crosstab_single(self, df):
      result = crosstab(df["A"], df["C"])
      expected = df.groupby(["A", "C"]).size().unstack()
      tm.assert_frame_equal(result, expected.fillna(0).astype(np.int64))
  
imports: import numpy
  import pytest
  import pandas
  from pandas import CategoricalDtype, CategoricalIndex, DataFrame, Index, MultiIndex, Series, crosstab
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestCrosstab obj's underlying member method code with example usage: obj.test_crosstab_single(df) without return types