In nowadays, the technical complexities of a website and variances to the browser make web testing and quality control much more difficult. This paper investigates the quality issue of the web systems and a systematic framework for web testing is proposed, in which a web application model is established to denote all components of a website by the Markov usage chain. To demonstrate its usability, a practical example of link validity testing is presented. The suggested validation mechanism not only generates automatically a complete set of the test scripts for link validation, but also provides quantitative analysis of the invalid components in a web application.