code: def test_stemming_unit(list_input):
      su_porter = units.Stemming()
      out_porter = su_porter.transform(list_input)
      assert "thi" in out_porter
      su_lancaster = units.Stemming(stemmer="lancaster")
      out_lancaster = su_lancaster.transform(list_input)
      assert "thi" in out_lancaster
      su_not_exist = units.Stemming(stemmer="fake_stemmer")
      with pytest.raises(ValueError):
          su_not_exist.transform(list_input)
  
imports: import pytest
  import numpy
  from matchzoo.preprocessors import units
  import matchzoo
  import tempfile
  import os
label_desc: Use image node_id 9 for calling a global function with example usage: test_stemming_unit(list_input) without return types