code: def test_index():
      cs = CoordinateSystem("ijk")
      assert cs.index("i") == 0
      assert cs.index("j") == 1
      assert cs.index("k") == 2
      pytest.raises(ValueError, cs.index, "x")
  
imports: from types import SimpleNamespace
  import numpy
  import pytest
  from ..coordinate_system import CoordinateSystem, CoordinateSystemError, CoordSysMaker, CoordSysMakerError, is_coordsys, is_coordsys_maker, product, safe_dtype
label_desc: Use image node_id 8 for calling a global function with example usage: test_index() without return types