An external web service may evolve without prior notification. In the course of the regression testing of a workflow-based web service, existing test case prioritization techniques may only verify the latest service composition using the not-yet-executed test cases, overlooking high-priority test cases that have already been applied to the service composition before the evolution. In this paper, we propose Preemptive Regression Testing (PRT), an adaptive testing approach to addressing this challenge. Whenever a change in the coverage of any service artifact is detected, PRT recursively preempts the current session of regression test, creates a sub-session of the current test session to assure such lately identified changes in coverage, and then resumes the execution of the suspended regression test session with a modified execution priority of the test cases in the test suite. PRT terminates only when each test case in the test suite has been executed at least once without any preemption activated in between any test case executions. The experimental result confirms that testing workflow-based web service in the face of such changes is very challenging; and one of the PRT techniques shows its potential to overcome the challenge. Keywords: evolving service composition, adaptive regression testing

1. This research is supported in part by the General Research Fund and the Early Career Scheme of the Research Grants Council of Hong Kong (project nos. 111410, 123512, 716612, and 717811). 2. IBM Research – China, Beijing, China. 3. Department of Computer Science, City University of Hong Kong, Tat Chee Avenue, Hong Kong. 4. Department of Computer Science, The University of Hong Kong, Pokfulam, Hong Kong. 5. (Corresponding author.) School of Computer Science and Engineering, Beihang University, Beijing, China. Email:

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