input: Write a function to create an instance of the "sru" class from the provided Python API for KB SRU 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 search results. If no collection is specified, the function should raise an Exception indicating an unknown collection.
  
  
  def perform_search(query, collection=False, startrecord=1, maximumrecords=1, recordschema=False):
      sru_instance = sru()
      response_obj = sru_instance.search(query, collection=collection, startrecord=startrecord, maximumrecords=maximumrecords, recordschema=recordschema)
      if not response_obj:
          raise Exception('Unknown collection')
      return response_obj
  
  assert type(perform_search("example query", collection="ANP")) == response
  assert type(perform_search("example query", collection="DPO")) == response
  assert type(perform_search("example query", collection="GGC")) == response
  try:
      perform_search("example query", collection="Unknown")
  except Exception as e:
      assert str(e) == 'Unknown collection'
  
output: def perform_search(query, collection=False, startrecord=1, maximumrecords=1, recordschema=False):
      sru_instance = sru()
      response_obj = sru_instance.search(query, collection=collection, startrecord=startrecord, maximumrecords=maximumrecords, recordschema=recordschema)
      if not response_obj:
          raise Exception('Unknown collection')
      return response_obj