code: def test_keyterms(model=classify.Bo1Model):
      ix = create_index()
      with ix.searcher() as s:
          docnum = s.document_number(path="/a")
          keys = list(
              s.key_terms([docnum], "content", numterms=3, model=model)
          )
          assert [t[0] for t in keys] == [
              u("collision"),
              u("calculations"),
              u("damped"),
          ]
          keys = list(
              s.key_terms([docnum], "extra", numterms=3, model=model)
          )
          assert keys == []
  
file_path: whoosh/tests/test_classify.py
imports: from __future__ import with_statement
  from whoosh import analysis, classify, fields, formats, query, reading
  from whoosh.compat import u, text_type
  from whoosh.filedb.filestore import RamStorage
  from whoosh.util.testing import TempIndex
label_desc: Use image node_id 3 for calling a global function with example usage: test_keyterms(model) without return types