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Adequate System-Level Testing of Distributed Systems

Publication Type:



Department of Computer Science, University of Colorado, Boulder, CO, p.158 (2006)


Software testing is about risk management. Typically, engineers use test adequacy
criteria to balance the cost and efficacy of the testing activity. Test adequacy criteria are rules that provide an objective stopping condition on test input creation by defining a finite set of test requirements that must be satisfied. While adequacy criteria have been a focus of research activity for many years, existing testing criteria do not address the unique features of distributed applications. The contributions of this dissertation are: (1) a study of reported failure scenarios of seven distributed applications; (2) a novel testing technique based on discrete-event simulations that serves as a basis for adequacy criteria for distributed systems; (3) a fault-based analysis technique that allows testers to addresses the fundamental risks associated with using adequacy criteria; and (4) a case-study evaluation of the simulation-based and fault-based techniques.

The failure study involves the categorization of test inputs and observations
needed to replicate failures reported by users. The results show that failure-producing scenarios are amenable to categorization, that simple system topologies are likely to be quite effective, and that a significant proportion of failure-producing scenarios involve distributed inputs. Thus, the results confirm our intuition that distributed systems need their own class of adequacy criteria.

Rather than inventing a new specification formalism, we instead adapt the common
practice of using discrete-event simulations for the design and understanding of
distributed systems to testing. Our key observation is that these simulations can be
viewed as specifications of the expected behavior of the system. Using simulations to test the implementation of a system is therefore a matter of selecting inputs to cover the simulation according to some criterion, and then mapping the inputs into the implementation domain. As simulations are sequential programs themselves, virtually all black- and white-box criteria can be used with a simulation-based technique.

When using any adequacy criterion for testing, there is generally no way for
engineers to know a priori how effective a test suite or the criterion itself is going to be on their system. To mitigate this risk within the context of simulation-based testing, we propose a fault-based analysis technique that uses code mutation operators to create a set of incorrect simulations. Candidate test cases are executed against each of these specification mutants and the number killed is used as a surrogate measure of effectiveness.

We evaluate the simulation-based technique and the companion fault-based analysis
method on 28 implementations of three distributed systems. The results of these
experiments are striking. First, we confirm that discrete-event simulations can indeed
be used in testing, and that white-box techniques based on the simulation are both effective,
and cost-effective when compared to randomly selected test suites of the same size.
Second, in a significant advancement of the state of the art, we demonstrate the power
of the fault-based analyses by improving the effectiveness of adequate suites within each
criterion, and by predicting exactly the overall relationships between different criteria.

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