JMCTest: Automatically testing inter-method contracts in Java

Abstract

Over the years, Design by Contract (DbC) has evolved as a powerful concept for program documentation, testing, and verification. Contracts formally specify assertions on (mostly) object-oriented programs: pre- and postconditions of methods, class invariants, allowed call orders, etc. Missing in the long list of properties specifiable by contracts are, however, method correlations: DbC languages fall short on stating assertions relating methods. In this paper, we propose the novel concept of inter-method contract, allowing precisely for expressing method correlations. We present JMC as a language for specifying and JMCTest as a tool for dynamically checking inter-method contracts on Java programs. JMCTest fully automatically generates objects on which the contracted methods are called and the validity of the contract is checked. Using JMCTest, we detected that large Java code bases (e.g. JBoss, Java RT) frequently violate standard inter-method contracts. In comparison to other verification tools inspecting (some) inter-method contracts, JMCTest can find bugs that remain undetected by those tools.