Service-oriented computing (SOC) is a relatively new paradigm for developing software applications through the composition of software units called services. With services, software is no longer owned but offered remotely, within or across organisational borders. Currently, the dominant technology for implementing services is that of Web services. Since service requestors do not usually have access to the implementation source code, from their perspective, services are offered as black boxes. However, requestors need to verify first that provided services are trustworthy and implemented correctly before they are integrated into their own business-critical systems. The verification and testing of remote, third-party services involve unique considerations, since testing must be performed in a blackbox manner and at runtime.
Addressing the aforementioned concerns, the research work described in this thesis investigates the feasibility of testing Web services for functional correctness, especially at runtime. The aim is to introduce rigour and automation to the testing process, so that service requestors can verify Web services with correctness guarantees and with the aid of tools. Thus, formal methods are utilised to specify the functionality of Web services unambiguously, so that they are amenable to automated and systematic testing. The well-studied stream X-machine (SXM) formalism has been selected as suitable for modelling both the dynamic behavior and static data of Web services, while a proven testing method associated with SXMs is used to derive test sets that can verify the correctness of the implementations.
This research concentrates on testing stateful Web services, in which the presence of state makes their behaviour more complex and more difficult to specify and test. The nature of Web service state, its effect on service behaviour, and implications on service modelling and testing, are investigated. In addition, comprehensive techniques are described for deriving a stream X-machine specification of a Web service, and for subsequently testing its implementation for equivalence to the specification. Then, a collaborative approach that makes possible third-party Web service verification and validation is proposed, in which the service provider is required to supply a SXM specification of the service functionality along with the standard WSDL description of its interface. On top of that, techniques are proposed for service providers to include information that ground the abstract SXM specification to the concrete Web service implementation. Having these descriptions available, it is possible to automate at runtime not only test set generation but also test case execution on Web services. A tool has been developed as part of this work, which extends an existing SXM-based testing tool (JSXM). The tool supports the tester activities, consisting of generation of abstract test cases from the SXM specification and their execution on the Web service under test using the supplied grounding information. Practical Web service examples are also used throughout the thesis to demonstrate the proposed techniques.
