input: Write a function to create an instance of the "sru" class and perform a search using the "search" method, passing in a query string and optionally a collection name, start record number, maximum number of records to return, and record schema. The function should return a "response" object containing the results of the search.
  
  assert sru_search("test query") is not None
  assert sru_search("error", collection="UnknownCollection") is None
  assert sru_search("query", collection="ANP", startrecord=1, maximumrecords=10, recordschema="dcx") is not None
output: def sru_search(query, collection=None, startrecord=1, maximumrecords=10, recordschema=None):
      sru_instance = sru()
      try:
          response = sru_instance.search(query, collection, startrecord, maximumrecords, recordschema)
          return response
      except Exception:
          return None