Automatic Test Factoring for Java
Author(s)
Saff, David
Artzi, Shay
Perkins, Jeff H.
Ernst, Michael D.
Date Issued
June 8, 2005
Series/Report no.
Massachusetts Institute of Technology Computer Science and Artificial Intelligence Laboratory
Abstract
Test factoring creates fast, focused unit tests from slow system-widetests; each new unit test exercises only a subset of the functionalityexercised by the system test. Augmenting a test suite with factoredunit tests should catch errors earlier in a test run.One way to factor a test is to introduce 'mock' objects. If a testexercises a component T, which interacts with another component E (the'environment'), the implementation of E can be replaced by a mock.The mock checks that T's calls to E are as expected, and it simulatesE's behavior in response. We introduce an automatic technique fortest factoring. Given a system test for T and E, and a record of T'sand E's behavior when the system test is run, test factoring generatesunit tests for T in which E is mocked. The factored tests can isolatebugs in T from bugs in E and, if E is slow or expensive, improve testperformance or cost.We have built an implementation of automatic dynamic test factoring for theJava language. Our experimental data indicates that it can reduce therunning time of a system test suite by up to an order of magnitude.
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