code: def test_ngram_unit(list_input):
      ngram = units.NgramLetter()
      out = ngram.transform(list_input)
      assert "#a#" in out
      ngram = units.NgramLetter(reduce_dim=False)
      out = ngram.transform(list_input)
      assert len(out) == 9
  
imports: import pytest
  import numpy
  from matchzoo.preprocessors import units
  import matchzoo
  import tempfile
  import os
label_desc: Use image node_id 11 for calling a global function with example usage: test_ngram_unit(list_input) without return types