This paper describes a large, unabridged data-set of Java source code gathered and shared as part of the Merobase Component Finder project of the Software-Engineering Group at the University of Mannheim. It consists of the complete index used to drive the search engine, www.merobase.com, the vast majority1of the source code modules accessible through it, and a tool that enables researchers to efficiently browse the collected data. We describe the techniques used to collect, format and store the data set, as well as the core capabilities of the Merobase search engine such as classic keyword-based, interface-based and test-driven search. This data-set, which represents one of the largest searchable collections of source and binary modules available online, has been recently made available for download and use in further research projects. All files are available at http://merobase.informatik.uni-mannheim.de/sources/.

The prime obstacle to automated defect testing has always been the generation of "correct" results against which to judge the behavior of the system under test - the "oracle problem". So called "back-to-back" testing techniques that exploit the availability of multiple versions of a system to solve the oracle problem have mainly been restricted to very special, safety critical domains such as military and space applications since it is so expensive to manually develop the additional versions. However, a new generation of software search engines that can find multiple copies of software components at virtually zero cost promise to change this situation. They make it economically feasible to use the knowledge locked in reusable software components to dramatically improve the efficiency of the software testing process. In this paper we outline the basic ingredients of such an approach.