code: def test_names_sep(df_checks):
      """test output if names_sep"""
      actual = df_checks.explode_index(
          names_sep="_", level_names=["a", "b"]
      )
      expected = pd.DataFrame(
          {
              ("fam", "id"): [1, 1, 1, 2, 2, 2, 3, 3, 3],
          }
      )
      expected.columns.names = ["a", "b"]
      assert_frame_equal(actual, expected)
  
file_path: pyjanitor/tests/functions/test_explode_index.py
imports: import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 11 for calling a global function with example usage: test_names_sep(df_checks) without return types