1. A method in a computing device having a memory and a processor for introducing spam into a search engine for testing purposes without affecting the search engine for non-testing purposes, the method comprising: providing an original data structure of the search engine, the original data structure including an original index of an original web graph; prior to receiving any query for testing purposes, receiving from a tester a specification of spam to be introduced into the data structure of the search engine, wherein the specification of spam received from the tester is used to generate search results in response to a query, and the specification of spam indicating an auxiliary web graph; generating an auxiliary data structure that represents the specified spam, the auxiliary data structure including an auxiliary index of the auxiliary web graph and after generating the auxiliary data structure, receiving a query for testing purposes, and generating search results for the received query based on an aggregation of information of the original data structure and the auxiliary data structure, wherein the search results are affected by the introduced spam without introducing spam into the original data structure and wherein the providing and generating are performed by the processor executing instructions stored in the memory.