Abstract
Server applications are expected to handle lower level faults and keep them from bringing down the whole system. Java provides a program-level exception handling mechanism in response to error conditions (that are translated into exceptions by Java VM). However, exception handling code is often widely scattered throughout an application and untested. This paper presents a program visualization tool ExTest that shows precisely all the handlers for exceptions triggered by certain kinds of operations, and for each of these handlers all the witness paths of how the operation would be triggered. Thus ExTest helps programmers understand the exception handling behavior of Java programs and also facilitates testing exception handling code.