Yoonsik Cheon

An overview of JML tools and applications

The Java Modeling Language (JML) can be used to specify the detailed design of Java classes and interfaces by adding annotations to Java source files. The aim of JML is to provide a specification language that is easy to use for Java programmers and that is supported by a wide range of tools for specification typechecking, runtime debugging, static analysis, and verification.This paper gives an overview of the main ideas behind JML, details about JML’s wide range of tools, and a glimpse into existing applications of JML.

Model Variables: Cleanly Supporting Abstraction in Design By Contract

In design by contract (DBC), assertions are typically written using program variables and query methods. The lack of separation between program code and assertions is confusing, because readers do not know what code is intended for use in the program and what code is only intended for specification purposes. This lack of separation also creates a potential runtime performance penalty, even when runtime assertion checks are disabled, due to both the increased memory footprint of the program and the execution of code maintaining that part of the programs state intended for use in specifications. To solve these problems, we present a new way of writing and checking DBC assertions without directly referring to concrete program states, using ‘model’, i.e. specification‐only, variables and methods. The use of model variables and methods does not incur the problems mentioned above, but it also allow one to write more easily assertions that are abstract, concise, and independent of representation details, and hence more readable and maintainable. We implemented these features in the runtime assertion checker for the Java Modeling Language (JML), but the approach could also be implemented in other DBC tools. Copyright

A Simple and Practical Approach to Unit Testing: The JML and JUnit Way

Writing unit test code is labor-intensive, hence it is often not done as an integral part of programming. However, unit testing is a practical approach to increasing the correctness and quality of software; for example, the Extreme Programming approach relies on frequent unit testing. In this paper we present a new approach that makes writing unit tests easier. It uses a formal specification languages runtime assertion checker to decide whether methods are working correctly, thus automating the writing of unit test oracles. These oracles can be easily combined with hand-written test data. Instead of writing testing code, the programmer writes formal specifications (e.g., pre- and postconditions). This makes the programmers task easier, because specifications are more concise and abstract than the equivalent test code, and hence more readable and maintainable. Furthermore, by using specifications in testing, specification errors are quickly discovered, so the specifications are more likely to provide useful documentation and inputs to other tools. We have implemented this idea using the Java Modeling Language (JML) and the JUnit testing framework, but the approach could be easily implemented with other combinations of formal specification languages and unit test tools.

The Larch/Smalltalk interface specification language

Object-oriented programming languages, such as Smalltalk, help to build reusable program modules. The reuse of program modules requires adequate documentation—formal or informal. Larch/Smalltalk is a formal specification language for specifying such reusable Smalltalk modules. Larch/Smalltalk firmly separates specification from implementation. In Larch/Smalltalk the unit of specification is an abstract data type, which is an abstraction of the behavior produced by one or more Smalltalk classes, A type can be a subtype of other types, which allows types to be organized based on specified behavior, and also allows for inheritance of their specifications. Larch/Smalltalk specifications are developed using specification tools integrated in the Smalltalk programming environment.

PWiseGen: Generating test cases for pairwise testing using genetic algorithms

Pairwise testing is a combinatorial testing technique that tests all possible pairs of input values. Although, finding a smallest set of test cases for pairwise testing is NP-complete, pairwise testing is regarded as a reasonable cost-benefit compromise among combinatorial testing methods. In this paper we formulate the problem of finding a pairwise test set as a search problem and apply a genetic algorithm to solve it. We also describe an open-source tool called PWiseGen for generating pairwise test sets. PWiseGen produces competitive results compared with existing pairwise testing tools. Besides, it provides a framework and a research platform for generating pairwise test sets using genetic algorithms; it is configurable, extensible, and reusable.

Specifying and checking method call sequences of Java programs

In a pre and postcondition-style specification, it is difficult to specify the allowed sequences of method calls, referred to as protocols. The protocols are essential properties of reusable object-oriented classes and application frameworks, and the approaches based on the pre and postconditions, such as design by contracts (DBC) and formal behavioral interface specification languages (BISL), are being accepted as a practical and effective tool for describing precise interfaces of (reusable) program modules. We propose a simple extension to the Java Modeling Language (JML), a BISL for Java, to specify protocol properties in an intuitive and concise manner. The key idea of our approach is to separate protocol properties from functional properties written in pre and post-conditions and to specify them in a regular expression-like notation. The semantics of our extension is formally defined and provides a foundation for implementing runtime checks. Case studies have been performed to show the effectiveness our approach. We believe that our approach can be adopted by other BISLs.

Preliminary Design of Larch/C++

We describe the problems encountered in the design of Larch/C++, especially its object-oriented features. We discuss a range of possible solutions to these problems, and give the rationale for our particular solutions. We also present examples of Larch/C++ specifications and discuss differences from Larch/C.

Automating Java Program Testing Using OCL and AspectJ

Random testing can eliminate subjectiveness in constructing test data and increase the diversity of test data. However, one difficult problem is to construct test oracles that decide test results---test failures or successes. Assertions can be used as test oracles and are most effective when they are derived from formal specifications such as OCL constraints. Random testing, if fully automated, can reduce the cost of testing dramatically. We propose an automated testing approach for Java programs by combining random testing and OCL. The key idea of our approach is to use OCL constraints as test oracles by translating them to runtime checks written in AspectJ. We implement our approach by adapting existing frameworks for translating OCL to AspectJ and assertion-based random testing. We evaluate the effectiveness of our approach through case studies and experiments. The results are encouraging in that our approach can detect errors in both implementations and OCL constraints and provide a practical means for using OCL.

A New Eclipse-Based JML Compiler Built Using AST Merging

The Java Modeling Language (JML) is a formal interface specification language to document the behavior of Java program modules and has been used in many research and industrial projects. However, its inability to support Java 5 features such as generics is reducing its user base significantly. Besides, the JML compiler is on average 8.5 times slower than the javac Java compiler. In this paper, we present a new JML compiler built on the Eclipse Java compiler to support Java 5 features. We used a technique called \emph{AST merging} to implement coarse-grained incremental compilation. In our experiments we observed a significant improvement in compilation speed, the new compiler is 3 to 4.5 times faster than the current one.

Abstraction in Assertion-Based Test Oracles

Assertions can be used as test oracles. However, writing effective assertions of right abstraction levels is difficult because on the one hand, detailed assertions are preferred for thorough testing (i.e., to detect as many errors as possible), but on the other hand abstract assertions are preferred for readability, maintainability, and reusability. As assertions become a practical tool for testing and debugging programs, this is an important and practical problem to solve for the effective use of assertions. We advocate the use of model variables - specification-only variables of which abstract values are given as mappings from concrete program states - to write abstract assertions for test oracles. We performed a mutation testing experiment to evaluate the effectiveness of the use of model variables in assertion-based test oracles. According to our experiment, assertions written in terms of model variables are as effective as assertions written without using model variables in detecting (injected) faults, and the execution time overhead of model variables are negligible. Our findings are applicable to other use of runtime checkable assertions.