Search-Based Test Input Generation for String Data Types Using the Results of Web Queries

Generating realistic, branch-covering string inputs is a challenging problem, due to the diverse and complex types of real-world data that are naturally encodable as strings, for example resource locators, dates of different localised formats, international banking codes, and national identity numbers. This paper presents an approach in which examples of inputs are sought from the Internet by reformulating program identifiers into web queries. The resultant URLs are downloaded, split into tokens, and used to augment and seed a search-based test data generation technique. The use of the Internet as part of test input generation has two key advantages. Firstly, web pages are a rich source of valid inputs for various types of string data that may be used to improve test coverage. Secondly, the web pages tend to contain realistic, human-readable values, which are invaluable when test cases need manual confirmation due to the lack of an automated oracle. An empirical evaluation of the approach is presented, involving string input validation code from 10 open source projects. Well-formed, valid string inputs were retrieved from the web for 96% of the different string types analysed. Using the approach, coverage was improved for 75% of the Java classes studied by an average increase of 14%.