Abstract
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Search services are the main interface through which people discover information on the Internet. A
fundamental challenge in testing search services is the lack of oracles. The sheer volume of data on the
Internet prohibits testers from verifying the results. Furthermore, it is difficult to objectively assess the
ranking quality because different assessors can have very different opinions on the relevance of a Web
page to a query. This paper presents a novel method for automatically testing search services without
the need of a human oracle. The experimental findings reveal that some commonly used search engines,
including Google, Yahoo!, and Live Search, are not as reliable as what most users would expect. For
example, they may fail to find pages that exist in their own repositories, or rank pages in a way that is
logically inconsistent. Suggestions are made for search service providers to improve their service quality.