Testing web services impose many challenges to existing testing methods, techniques, and tools; especially those available to traditional applications. Composed web services increase these challenges by requiring additional validation and verification efforts. Structural-based testing approaches have been thoroughly researched for traditional applications; however, they have not yet been examined, as a methodology, for testing composed web services. In this work, we introduce a formal model for an abstract-based workflow framework that can be used to capture a composed web service under test. We then define a set of applicable structural-based testing criteria to the framework. Finally we outline a promising line of testing criteria that can be applied to this framework.