arXiv subjects

Serge Demeyer

Publications and source records attributed to Serge Demeyer.

At least 19 recordsLinked to original sources

arXiv2026

DJPlus: Generating minimal test suites for strong coverage criteria in graph models

Automated test generation from graph models is essential to model-based testing. In this type of testing, graph coverage ensures test suite strength but also results in long test cases that take time to execute on the system under test. We propose a novel optimization-driven method, DJPlus, which generates reduced test suites while satisfying given graph-based test requirements. We implement DJPlus and show the feasibility of edge-pair criterion, a stronger coverage criterion than vertex or edge criteria, on four realistic systems, while prime path criterion poses scalability issues. Our evaluation reveals that the alternative methods generate 2 to 26 times more redundant test steps than DJPlus and DJPlus decreases test execution times by reducing the number of test steps. These results show that DJPlus is a positive step towards tackling the challenges of model-based testing at an industrial scale.

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arXiv2026

RESTCov: A Tool for Structural Coverage Analysis of REST APIs

REST APIs are widely used in modern software systems, but developers and testers often lack visibility into which parts of an API specification are exercised by a test suite. Traditional coverage analysis usually relies on source-code instrumentation, which is impractical for REST APIs that are distributed, externally maintained, and hence accessible only through black-box execution. This paper presents RESTCov, a lightweight tool that computes structural REST API coverage from an OpenAPI specification and observed HTTP request/response logs, reporting coverage across paths, operations, parameters, media types, status codes, and status classes. RESTCov produces both machine-readable results and a human-readable HTML report, helping users inspect coverage gaps, diagnose specification-log mismatches, and evaluate REST API test suites without requiring access to the implementation. Screencast: https://youtu.be/mNz2P43OyUc Repository: https://github.com/2tolgahan2/RESTCov

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arXiv2026

Mutation Testing of Simulink Cyber-Physical System Models: Challenges and Solutions in Practice

Several experience reports illustrate that mutation testing is capable of supporting a shift-left testing strategy, especially in industries where late bug discovery incurs very high costs and risks. In the context of cyber-physical systems, a shift left implies that engineers need to test the design models used to simulate, prototype, and analyse the feasibility of the system under design. In this paper, we analyse the challenges we encountered and the lessons we learned when incorporating mutation testing in the context of DUCO, a company producing ventilation systems for buildings. The engineers within DUCO have years of experience with model-based engineering centered around Simulink and StateFlow, including unit tests for their models. During a pilot project with our tool prototype MUT4SLX we learned that equivalent mutants, requirement traceability, and mutation testing for Stateflow represent particular challenges not yet reported in the academic literature.

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arXiv2025

Agentic LLMs for REST API Test Amplification: A Comparative Study Across Cloud Applications

Representational State Transfer (REST) APIs are a cornerstone of modern cloud native systems. Ensuring their reliability demands automated test suites that exercise diverse and boundary level behaviors. Nevertheless, designing such test cases remains a challenging and resource intensive endeavor. This study extends prior work on Large Language Model (LLM) based test amplification by evaluating single agent and multi agent configurations across four additional cloud applications. The amplified test suites maintain semantic validity with minimal human intervention. The results demonstrate that agentic LLM systems can effectively generalize across heterogeneous API architectures, increasing endpoint and parameter coverage while revealing defects. Moreover, a detailed analysis of computational cost, runtime, and energy consumption highlights trade-offs between accuracy, scalability, and efficiency. These findings underscore the potential of LLM driven test amplification to advance the automation and sustainability of REST API testing in complex cloud environments.

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arXiv2025

Test Amplification for REST APIs via Single and Multi-Agent LLM Systems

REST APIs (Representational State Transfer Application Programming Interfaces) play a vital role in modern cloud-native applications. As these APIs grow in complexity and scale, ensuring their correctness and robustness becomes increasingly important. Automated testing is essential for identifying hidden bugs, particularly those that appear in edge cases or under unexpected inputs. However, creating comprehensive and effective test suites for REST APIs is challenging and often demands significant effort. In this paper, we investigate the use of large language model (LLM) systems, both single-agent and multi-agent setups, for amplifying existing REST API test suites. These systems generate additional test cases that aim to push the boundaries of the API, uncovering behaviors that might otherwise go untested. We present a comparative evaluation of the two approaches across several dimensions, including test coverage, bug detection effectiveness, and practical considerations such as computational cost and energy usage. Our evaluation demonstrates increased API coverage, identification of numerous bugs in the API under test, and insights into the computational cost and energy consumption of both approaches.

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arXiv2025

Test Amplification for REST APIs Using "Out-of-the-box" Large Language Models

REST APIs (Representational State Transfer Application Programming Interfaces) are an indispensable building block in today's cloud-native applications, so testing them is critically important. However, writing automated tests for such REST APIs is challenging because one needs strong and readable tests that exercise the boundary values of the protocol embedded in the REST API. In this paper, we report our experience with using "out of the box" large language models (ChatGPT and GitHub's Copilot) to amplify REST API test suites. We compare the resulting tests based on coverage and understandability, and we derive a series of guidelines and lessons learned concerning the prompts that result in the strongest test suite.

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arXiv2025

Cross-System Categorization of Abnormal Traces in Microservice-Based Systems via Meta-Learning

Microservice-based systems (MSS) may fail with various fault types. While existing AIOps methods excel at detecting abnormal traces and locating the responsible service(s), human efforts are still required for diagnosing specific fault types and failure causes.This paper presents TraFaultDia, a novel AIOps framework to automatically classify abnormal traces into fault categories for MSS. We treat the classification process as a series of multi-class classification tasks, where each task represents an attempt to classify abnormal traces into specific fault categories for a MSS. TraFaultDia leverages meta-learning to train on several abnormal trace classification tasks with a few labeled instances from a MSS, enabling quick adaptation to new, unseen abnormal trace classification tasks with a few labeled instances across MSS. TraFaultDia's use cases are scalable depending on how fault categories are built from anomalies within MSS. We evaluated TraFaultDia on two MSS, TrainTicket and OnlineBoutique, with open datasets where each fault category is linked to faulty system components (service/pod) and a root cause. TraFaultDia automatically classifies abnormal traces into these fault categories, thus enabling the automatic identification of faulty system components and root causes without manual analysis. TraFaultDia achieves 93.26% and 85.20% accuracy on 50 new classification tasks for TrainTicket and OnlineBoutique, respectively, when trained within the same MSS with 10 labeled instances per category. In the cross-system context, when TraFaultDia is applied to a MSS different from the one it is trained on, TraFaultDia gets an average accuracy of 92.19% and 84.77% for the same set of 50 new, unseen abnormal trace classification tasks of the respective systems, also with 10 labeled instances provided for each fault category per task in each system.

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arXiv2023

A Digital Twin Description Framework and its Mapping to Asset Administration Shell

The pace of reporting on Digital Twin (DT) projects continues to accelerate both in industry and academia. However, these experience reports often leave out essential characteristics of the DT, such as the scope of the system-under-study, the insights and actions enabled, and the time-scale of processing. A lack of these details could therefore hamper both understanding of these DTs and development of DT tools and techniques. Our previous work developed a DT description framework with fourteen characteristics as a checklist for experience report authors to better describe the capabilities of their DT projects. This report provides an extended example of reporting to highlight the utility of this description framework, focusing on the DT of an industrial drilling machine. Furthermore, we provide a mapping from our description framework to the Asset Administration Shell (AAS) which is an emerging standard for Industry 4.0 system integration. This mapping aids practitioners in understanding how our description framework relates to AAS, potentially aiding in description or implementation activities.

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arXiv2022

Mutation Testing Optimisations using the Clang Front-end

Mutation testing is the state-of-the-art technique for assessing the fault detection capacity of a test suite. Unfortunately, a full mutation analysis is often prohibitively expensive. The CppCheck project for instance, demands a build time of 5.8 minutes and a test execution time of 17 seconds on our desktop computer. An unoptimised mutation analysis, for 55,000 generated mutants took 11.8 days in total, of which 4.3 days is spent on (re)compiling the project. In this paper we present a feasibility study, investigating how a number of optimisation strategies can be implemented based on the Clang front-end. These optimisation strategies allow to eliminate the compilation and execution overhead in order to support efficient mutation testing for the C language family. We provide a proof-of-concept tool that achieves a speedup of between 2x and 30x. We make a detailed analysis of the speedup induced by the optimisations, elaborate on the lessons learned and point out avenues for further improvements.

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arXiv2022

Small-Amp: Test Amplification in a Dynamically Typed Language

Some test amplification tools extend a manually created test suite with additional test cases to increase the code coverage. The technique is effective, in the sense that it suggests strong and understandable test cases, generally adopted by software engineers. Unfortunately, the current state-of-the-art for test amplification heavily relies on program analysis techniques which benefit a lot from explicit type declarations present in statically typed languages. In dynamically typed languages, such type declarations are not available and as a consequence test amplification has yet to find its way to programming languages like Smalltalk, Python, Ruby and Javascript. We propose to exploit profiling information --readily obtainable by executing the associated test suite-- to infer the necessary type information creating special test inputs with corresponding assertions. We evaluated this approach on 52 selected test classes from 13 mature projects in the Pharo ecosystem containing approximately 400 test methods. We show the improvement in killing new mutants and mutation coverage at least in 28 out of 52 test classes (53%). Moreover, these generated tests are understandable by humans: 8 out of 11 pull-requests submitted were merged into the main code base (72%). These results are comparable to the state-of-the-art, hence we conclude that test amplification is feasible for dynamically typed languages.

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arXiv2021

AmPyfier: Test Amplification in Python

Test Amplification is a method to extend handwritten tests into a more rigorous test suite covering corner cases in the system under test. Unfortunately, the current state-of-the-art for test amplification heavily relies on program analysis techniques which benefit a lot from explicit type declarations present in statically typed languages like Java and C++. In dynamically typed languages, such type declarations are not available and as a consequence test amplification has yet to find its way to programming languages like Python, Ruby and Javascript. In this paper, we present AmPyfier, a proof-of-concept tool, which brings test amplification to the dynamically typed, interpreted language Python. We evaluated this approach on 7 open-source projects, and found that AmPyfier could successfully strengthen 7 out of 10 test classes (70%). As such we demonstrate that test amplification is feasible for one of the most popular programming languages in use today.

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arXiv2021

Mutant Density: A Measure of Fault-Sensitive Complexity

Software code complexity is a well-studied property to determine software component health. However, the existing code complexity metrics do not directly take into account the fault-proneness aspect of the code. We propose a metric called mutant density where we use mutation as a method to introduce artificial faults in code, and count the number of possible mutations per line. We show how this metric can be used to perform helpful analysis of real-life software projects.

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arXiv2021

Comparing Mutation Coverage Against Branch Coverage in an Industrial Setting

The state-of-the-practice in software development is driven by constant change fueled by continuous integration servers. Such constant change demands for frequent and fully automated tests capable to detect faults immediately upon project build. As the fault detection capability of the test suite becomes so important, modern software development teams continuously monitor the quality of the test suite as well. However, it appears that the state-of-the-practice is reluctant to adopt strong coverage metrics (namely mutation coverage), instead relying on weaker kinds of coverage (namely branch coverage). In this paper, we investigate three reasons that prohibit the adoption of mutation coverage in a continuous integration setting: (1) the difficulty of its integration into the build system, (2) the perception that branch coverage is "good enough", and (3) the performance overhead during the build. Our investigation is based on a case study involving four open source systems and one industrial system. We demonstrate that mutation coverage reveals additional weaknesses in the test suite compared to branch coverage and that it is able to do so with an acceptable performance overhead during project build.

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arXiv2020

Software Test Automation Maturity -- A Survey of the State of the Practice

The software industry has seen an increasing interest in test automation. In this paper, we present a test automation maturity survey serving as a self-assessment for practitioners. Based on responses of 151 practitioners coming from above 101 organizations in 25 countries, we make observations regarding the state of the practice of test automation maturity: a) The level of test automation maturity in different organizations is differentiated by the practices they adopt; b) Practitioner reported the quite diverse situation with respect to different practices, e.g., 85\% practitioners agreed that their test teams have enough test automation expertise and skills, while 47\% of practitioners admitted that there is lack of guidelines on designing and executing automated tests; c) Some practices are strongly correlated and/or closely clustered; d) The percentage of automated test cases and the use of Agile and/or DevOps development models are good indicators for a higher test automation maturity level; (e) The roles of practitioners may affect response variation, e.g., QA engineers give the most optimistic answers, consultants give the most pessimistic answers. Our results give an insight into present test automation processes and practices and indicate chances for further improvement in the present industry.

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arXiv2020

Do Null-Type Mutation Operators Help Prevent Null-Type Faults?

The null-type is a major source of faults in Java programs, and its overuse has a severe impact on software maintenance. Unfortunately traditional mutation testing operators do not cover null-type faults by default, hence cannot be used as a preventive measure. We address this problem by designing four new mutation operators which model null-type faults explicitly. We show how these mutation operators are capable of revealing the missing tests, and we demonstrate that these mutation operators are useful in practice. For the latter, we analyze the test suites of 15 open-source projects to describe the trade-offs related to the adoption of these operators to strengthen the test suite.

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arXiv2020

C++11/14 Mutation Operators Based on Common Fault Patterns

The C++11/14 standard offers a wealth of features aimed at helping programmers write better code. Unfortunately, some of these features may cause subtle programming faults, likely to go unnoticed during code reviews. In this paper we propose four new mutation operators for C++11/14 based on common fault patterns, which allow to verify whether a unit test suite is capable of testing against such faults. We validate the relevance of the proposed mutation operators by performing a case study on seven real-life software systems.

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arXiv2018

Goal-Oriented Mutation Testing with Focal Methods

Mutation testing is the state-of-the-art technique for assessing the fault-detection capacity of a test suite. Unfortunately, mutation testing consumes enormous computing resources because it runs the whole test suite for each and every injected mutant. In this paper we explore fine-grained traceability links at method level (named focal methods), to reduce the execution time of mutation testing and to verify the quality of the test cases for each individual method, instead of the usually verified overall test suite quality. Validation of our approach on the open source Apache Ant project shows a speed-up of 573.5x for the mutants located in focal methods with a quality score of 80%.

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arXiv2018

Dynamic Mutant Subsumption Analysis using LittleDarwin

Many academic studies in the field of software testing rely on mutation testing to use as their comparison criteria. However, recent studies have shown that redundant mutants have a significant effect on the accuracy of their results. One solution to this problem is to use mutant subsumption to detect redundant mutants. Therefore, in order to facilitate research in this field, a mutation testing tool that is capable of detecting redundant mutants is needed. In this paper, we describe how we improved our tool, LittleDarwin, to fulfill this requirement.

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