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 the "response" object containing the search results, and assert the correctness of the function with given test cases.
  
  
  def perform_sru_search(query, collection=None, startrecord=1, maximumrecords=1, recordschema=None):
      sru_instance = sru()
      response_obj = sru_instance.search(query, collection, startrecord, maximumrecords, recordschema)
      return response_obj
  
  # Test cases
  assert perform_sru_search("cats", "DPO").nr_of_records >= 0
  assert perform_sru_search("dogs", "ANP", 1, 5).nr_of_records >= 0
  assert perform_sru_search("history", "BYVANCK", 1, 10).nr_of_records >= 0
  assert perform_sru_search("science", "SGD", 1, 2, "dcx").nr_of_records >= 0
  assert perform_sru_search("literature", "GGC", 1, 3, "dcx").nr_of_records >= 0
  assert perform_sru_search("").nr_of_records == 0
  
output: def perform_sru_search(query, collection=None, startrecord=1, maximumrecords=1, recordschema=None):
      sru_instance = sru()
      response_obj = sru_instance.search(query, collection, startrecord, maximumrecords, recordschema)
      return response_obj