code: def test_display_system(monkeypatch, dispnum):
      """Check that when only a $DISPLAY is defined, it is used"""
      config._display = None
      config._config.remove_option("execution", "display_variable")
      dispstr = ":%d" % dispnum
      monkeypatch.setenv("DISPLAY", dispstr)
      assert config.get_display() == dispstr
      # Test that it was correctly cached
      assert config.get_display() == dispstr
  
file_path: nipype/nipype/utils/tests/test_config.py
imports: import os
  import sys
  import pytest
  from nipype import config
  from unittest.mock import MagicMock
label_desc: Use image node_id 3 for calling a global function with example usage: test_display_system(monkeypatch, dispnum) without return types