code: def test_categorical_df_concat(self):
      inp = [
          pd.DataFrame(
              {
                  "A": pd.Series(["a", "b", "c"], dtype="category"),
                  "B": pd.Series([100, 102, 103], dtype="int64"),
                  "C": pd.Series(["x", "x", "x"], dtype="category"),
              }
          ),
          pd.DataFrame(
              {
                  "A": pd.Series(["c", "b", "d"], dtype="category"),
                  "B": pd.Series([103, 102, 104], dtype="int64"),
                  "C": pd.Series(["y", "y", "y"], dtype="category"),
              }
          ),
          pd.DataFrame(
              {
                  "A": pd.Series(["a", "b", "d"], dtype="category"),
                  "B": pd.Series([101, 102, 104], dtype="int64"),
                  "C": pd.Series(["z", "z", "z"], dtype="category"),
              }
          ),
      ]
      result = categorical_df_concat(inp)
  
      expected = pd.DataFrame(
          {
              "A": pd.Series(
                  ["a", "b", "c", "c", "b", "d", "a", "b", "d"],
                  dtype="category",
              ),
              "B": pd.Series(
                  [100, 102, 103, 103, 102, 104, 101, 102, 104],
                  dtype="int64",
              ),
              "C": pd.Series(
                  ["x", "x", "x", "y", "y", "y", "z", "z", "z"],
                  dtype="category",
              ),
          },
      )
      expected.index = pd.Int64Index([0, 1, 2, 0, 1, 2, 0, 1, 2])
      assert_equal(expected, result)
      assert_equal(
          expected["A"].cat.categories, result["A"].cat.categories
      )
      assert_equal(
          expected["C"].cat.categories, result["C"].cat.categories
      )
  
file_path: catalyst/tests/utils/test_pandas_utils.py
imports: import pandas
  from catalyst.testing import parameter_space, CatalystTestCase
  from catalyst.testing.predicates import assert_equal
  from catalyst.utils.pandas_utils import categorical_df_concat, nearest_unequal_elements
label_desc: Use image node_id 1 for calling the TestCatDFConcat obj's underlying member method code with example usage: obj.test_categorical_df_concat() without return types