code: def test_insert_fallback_to_base_index():
      # https://github.com/pandas-dev/pandas/issues/47071
  
      idx = CustomIndex([1, 2, 3])
      result = idx.insert(0, "string")
      expected = Index(["string", 1, 2, 3], dtype=object)
      tm.assert_index_equal(result, expected)
  
      df = DataFrame(
          np.random.default_rng(2).standard_normal((2, 3)),
          columns=idx,
          index=Index([1, 2], name="string"),
      )
      result = df.reset_index()
      tm.assert_index_equal(result.columns, expected)
  
imports: import numpy
  from pandas import DataFrame, Index
  import pandas._testing
label_desc: Use image node_id 1 for calling a global function with example usage: test_insert_fallback_to_base_index() without return types