code: def test_nihon_duplicate_channels(monkeypatch):
      """Test deduplication of channel names."""
      fname = data_path / "NihonKohden" / "MB0400FU.EEG"
  
      def return_channel_duplicates(fname):
          ch_names = nihon._default_chan_labels
          ch_names[1] = ch_names[0]
          return ch_names
  
      monkeypatch.setattr(
          nihon, "_read_21e_file", return_channel_duplicates
      )
  
      assert len(nihon._read_21e_file(fname)) > len(
          set(nihon._read_21e_file(fname))
      )
      msg = (
          "Channel names are not unique, found duplicates for: "
          "{'FP1'}. Applying running numbers for duplicates."
      )
      with pytest.warns(RuntimeWarning, match=msg):
          read_raw_nihon(fname)
  
file_path: mne-python/mne/io/nihon/tests/test_nihon.py
imports: import pytest
  from numpy.testing import assert_array_almost_equal
  from mne.datasets import testing
  from mne.io import read_raw_edf, read_raw_nihon
  from mne.io.nihon import nihon
  from mne.io.nihon.nihon import _read_nihon_annotations, _read_nihon_header, _read_nihon_metadata
  from mne.io.tests.test_raw import _test_raw_reader
label_desc: Use image node_id 2 for calling a global function with example usage: test_nihon_duplicate_channels(monkeypatch) and returns: ch_names