In-Situ Concolic Testing of JavaScript

JavaScript (JS) has evolved into a versatile and popular programming language for not only the web, but also a wide range of server-side and client-side applications. Effective, efficient, and easy-to-use testing techniques for JS scripts are in great demand. In this paper, we introduce a holistic approach to applying concolic testing to JS scripts in-situ, i.e., JS scripts are executed in their native environments as part of concolic execution and test cases generated are directly replayed in these environments. We have implemented this approach in the context of Node.js, a JS runtime built on top of Chrome’s V8 JS engine, and evaluated its effectiveness and efficiency through application to 180 Node.js libraries with heavy use of string operations. For 85% of these libraries, it achieved statement coverage ranging between 75% and 100%, a close match in coverage with the hand-crafted unit test suites accompanying their NPM releases. Our approach detected numerous exceptions in these libraries. We analyzed the exception reports for 12 representative libraries and found 6 bugs in these libraries, 4 of which are previously undetected. The bug reports and patches that we filed for these bugs have been accepted by the library developers on GitHub.