A Generalized Approach for Solving Web Form Constraints

Summary

When creating automated tests for web applications, one major part is filling and submitting web forms. Filling out forms automatically is challenging, as form fields would typically be subject to specific constraints that prevent entry of invalid data. Modern test generators, such as the recently proposed Black Ostrich scanner, are already capable of identifying expected patterns for form values and solve them, using instance generators for regular expressions and/or string constraint solvers. String solvers, however, are limited to, well, strings. We present FormWhisperer, a fully automated solution for testing web pages containing forms. It is able to extract and solve complex constraints on form input values, such as arithmetic constraints or relations between multiple form fields. FormWhisperer symbolically analyzes the HTML and JavaScript code of a web page to automatically extract a language specification that captures syntax and semantics of the form fields. This language specification can be used as is to generate test inputs that are valid syntactically and semantically; on top, it can also validate inputs independently; and it is human-readable, meaning that it can be edited and maintained by developers, or used in documentation.