code: def test_format_index_with_na_rep():
      df = DataFrame(
          [[1, 2, 3, 4, 5]], columns=["A", None, np.nan, NaT, NA]
      )
      ctx = df.style.format_index(None, na_rep="--", axis=1)._translate(
          True, True
      )
      assert ctx["head"][0][1]["display_value"] == "A"
      for i in [2, 3, 4, 5]:
          assert ctx["head"][0][i]["display_value"] == "--"
  
imports: import numpy
  import pytest
  from pandas import NA, DataFrame, IndexSlice, MultiIndex, NaT, Timestamp, option_context
  from pandas.io.formats.style import Styler
  from pandas.io.formats.style_render import _str_escape
label_desc: Use image node_id 12 for calling a global function with example usage: test_format_index_with_na_rep() without return types