code: def test_combine():
      schema = fields.Schema(
          id=fields.ID(stored=True), value=fields.TEXT
      )
      ix = RamStorage().create_index(schema)
      w = ix.writer()
      w.add_document(id=u("1"), value=u("alfa bravo charlie all"))
      w.add_document(id=u("2"), value=u("bravo charlie echo all"))
      w.add_document(id=u("3"), value=u("charlie echo foxtrot all"))
      w.add_document(id=u("4"), value=u("echo foxtrot india all"))
      w.add_document(id=u("5"), value=u("foxtrot india juliet all"))
      w.add_document(id=u("6"), value=u("india juliet alfa all"))
      w.add_document(id=u("7"), value=u("juliet alfa bravo all"))
      w.add_document(id=u("8"), value=u("charlie charlie charlie all"))
      w.commit()
  
      with ix.searcher() as s:
  
          def idsof(r):
              return "".join(hit["id"] for hit in r)
  
          def check(r1, methodname, r2, ids):
              getattr(r1, methodname)(r2)
              assert idsof(r1) == ids
  
          def rfor(t):
              return s.search(query.Term("value", t))
  
          assert idsof(rfor(u("foxtrot"))) == "345"
          check(rfor(u("foxtrot")), "extend", rfor("charlie"), "345812")
          check(rfor(u("foxtrot")), "filter", rfor("juliet"), "5")
          check(rfor(u("charlie")), "filter", rfor("foxtrot"), "3")
          check(rfor(u("all")), "filter", rfor("foxtrot"), "345")
          check(rfor(u("all")), "upgrade", rfor("india"), "45612378")
          check(
              rfor(u("charlie")),
              "upgrade_and_extend",
              rfor("echo"),
              "23814",
          )
  
imports: from __future__ import with_statement
  import pytest
  from whoosh import analysis, fields, formats, highlight, qparser, query
  from whoosh.codec.whoosh3 import W3Codec
  from whoosh.compat import u, xrange, text_type, permutations
  from whoosh.filedb.filestore import RamStorage
  from whoosh.util.testing import TempStorage, TempIndex
label_desc: Use image node_id 4 for calling a global function with example usage: test_combine() and returns: str, s