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Andreas Zeller

@AndreasZeller.mastodon.social.ap.brid.gy
13 followers 0 following 128 posts

Software researcher at cispa.de., working on fandango-fuzzer.github.io, www.cispa.de/s3, @TheFuzzingBook, @TheDebuggingBook, and more […] 🌉 bridged from ⁂ mastodon.social/@AndreasZeller, follow @ap.brid.gy to interact

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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 22/10/2026
"But do you find bugs with #Fandango?" You bet! This Summer, we reported more than 100 bugs and vulnerabilities to library and app maintainers. Here's a crash my student Norman Becker found in Apple Music using the #Fanbase audio specs we released on Tuesday: support.apple.com/en-mn/127115
About the security content of macOS Tahoe 26.5

This document describes the security content of macOS
Tahoe 26.5.

Additional recognition
Music
We would like to acknowledge Norman Becker for their assistance.
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 20/10/2026
Never Gonna Give You Up! This week, we're releasing five audio formats (WAV, FLAC, Ogg, MP3, and AAC) for #Fandango: use `fandango fuzz -F aac -n 1000` to generate 1,000 AAC files for testing. Unfortunately, Fandango can't synthesize Rick Astley - but it can definitely test your boundaries :-) […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 14/10/2026
How can you tailor a test generator to focus on specific software features? At #ASE2026 today, José Antonio "Pepe" Zamudio Amaya presents our "Compás" work on "feature-focused test generation". Talk details and paper here […] [Original post on mastodon.social]
Pepe in front of a conference poster "Feature-Focused Test Generation"
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 13/10/2026
New fuzzing formats for #Fandango! Today, we added HEIC, JXL, PPM, SVG, XBM, and XPM to the set of #Fanbase formats. Use `fandango fuzz -F heic -n 1000` to generate 1,000 HEIC files for testing. Special thanks to José Antonio "Pepe" Zamudio Amaya and Norman Becker for preparing this release […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 11/10/2026
At #ASE2026 tomorrow, visit these workshop presentations by my students Tural and Marius: * How Grammar-Based Synthetic Data Shapes Behavior Learning: An Empirical Study of Input Generation Strategies * Can Open-Weight LLMs Predict Test Outcomes from […] [Original post on mastodon.social]
* How Grammar-Based Synthetic Data Shapes Behavior Learning: An Empirical Study of Input Generation Strategies

* Can Open-Weight LLMs Predict Test Outcomes from Traces? A Cross-Subject Boundary Study on Tests4Py

* Failure Explanations: The Missing Abstraction between Debugging and Repair

* Execution Features and Their Relations to Faults: A Replication on Defects4J
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 11/10/2026
Talk slides and details for "On Impact in Software Engineering Research" are now available. See you on Monday at #ASE2026: conf.researchr.org/details/ase-2026…
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 11/10/2026
Talk slides and details for "The Devil's Guide to Doing your PhD" are now available. See you on Monday at #ASE2026! conf.researchr.org/details/ase-2026…
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 09/10/2026
Advice to young researchers! On Monday at #ASE2026 in Munich, I will be giving two talks: * "The Devil's Guide to Doing your PhD" at the Doctoral Symposium; and * "On Impact in Software Engineering Research" at the New Faculty Symposium. Will post all slides after the talks. Meet me at ASE!
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 06/10/2026
Introducing #Fanbase - a curated collection of #Fandango file format specifications: Use `fandango fuzz -F png -n 1000` to generate 1,000 PNG files for testing. Starting with PNG, GIF, JPG, and other image formats today; more formats every Tuesday. Enjoy! github.com/fandango-fuzzer/fanbase
github.com
GitHub - fandango-fuzzer/fanbase: A collection of Fandango input specifications (grammars) for many file formats.
A collection of Fandango input specifications (grammars) for many file formats. - fandango-fuzzer/fanbase
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 27/08/2026
I will be presenting our latest #Fandango work at the #GOTO conference on September 30 in Copenhagen, Denmark. Let's meet at GOTO! gotocph.com/2026
This is a talk announcement.

GOTO Copenhagen • Sep 28 - Oct 2, 2026
goto;

Fuzzing your way to better test inputs

Andreas Zeller
Faculty at CISPA Helmholtz Center for Information Security

gotocph.com
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 24/08/2026
The #Fandango team is pulling off a long evening session because their advisor insists that the paper be ready one day _before_ the deadline
Evening dinner with the Fandango team
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 20/08/2026
On my way to Bochum for the PhD exam of Niklas Risse (with co-examiners Marcel Böhme and Michael Pradel)
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 06/08/2026
Proud greetings from the 💃 #Fandango headquarters! The all-new 1.2 release of our specification-guided #Fandango fuzzer brings many under-the-hood improvements, along with new, useful user-facing features and documentation. Check out the release notes! […] [Original post on mastodon.social]
Norman Becker, Valentin Huber, and Tim Scheckenbach in the Fandango HQ office. The empty seats belong to Alexander Liggesmeyer and José Antonio Zamudio Amaya, two more great members of the #Fandango team.
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 31/07/2026
At #Dagstuhl with my team and a few guests, setting our research agenda for the next 12 months. Big things coming!
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 28/07/2026
There's an ICSE 2020 paper of mine, "Debugging Inputs", that, according to Google Scholar, has a whopping 12,800 citations. Most cited paper ever? Alas, ACM DL is closer to the truth with 1 citation (actually, a self-citation). Does anyone know how to report wrong numbers to the Google Scholar team?
Screenshot of Google Scholar, listing 12,832 citations; and contrasting screenshot of ACM DL, listing 1 citation for the same article.
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 21/07/2026
In the past months, I have had a number of great PhD students pass their exams: * Leon Bettscheider for "Input Grammars in Practice - Methods for Symbolic Mining, Systematic Evaluation, and Grey-Box Testing": scholar.google.com/citations?user=G… * Masudul Hasan […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 17/07/2026
I have been selected into the inaugural class of the ACM SIGSOFT Software Engineering Academy: www2.sigsoft.org/academy/inaugural-…
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 09/07/2026
Besides code coverage, there are several execution features that can correlate with failure and thus help in localizing faults. See the talk of Marius Smytzek today 15:00 at #FSE2026 […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 08/07/2026
Are you into program repair or automated debugging? Today at #FSE2026 - Two presentations by Marius Smytzek on how to boost fault localization: * 12:10 conf.researchr.org/details/fse-2026… * 16:30 […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 07/07/2026
Reunited after 20 years! These are Jacek Śliwerski, Tom Zimmermann, and Andreas Zeller, meeting twenty years after creating the foundational #SZZ algorithm to relate bugs to associated changes. See us telling the story of the work in our impact paper award […] [Original post on mastodon.social]
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 06/07/2026
Today at noon at #SSBSE2026, see how we use Search-Based Testing to quickly solve complex input constraints in the #Fandango project – orders of magnitude faster than with traditional constraint solvers. With José Antonio "Pepe" Zamudio Amaya and Marius Smytzek […]
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Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 06/07/2026
Today at 12:15 in the #FSE2026 doctoral symposium: My PhD student Alexander Liggesmeyer presents his work on protocol testing and fuzzing with #Fandango: conf.researchr.org/details/fse-2026… Paper available!
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 06/07/2026
Today at 10:05 at #AIWARE2026: Norman Becker asks, "Can LLMs Really Reason about Code?" 2026.aiwareconf.org/details/aiware-… This exciting work was done with Tural Mammadov; paper and slides […]
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 05/07/2026
Today at #FSE2026 in Montreal: A 180-minute tutorial on our next generation #Fandango fuzzer, bringing high quality input generation to a program near you. See you 14:00-17:30 in Concordia SGW Campus, Room MB 2.430 More about #Fandango: fandango-fuzzer.github.io Room info […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 03/07/2026
Back again! Five weeks ago, an artificial lens in my right eye had dislocated itself; I was effectively one-eyed, and my doctors strongly discouraged me from reading - so, lots of talking and phoning, but only the most important mails, and no papers at all. I […] [Original post on mastodon.social]
Andreas Zeller in a hospital gown with a large white patch over his right eye
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 22/05/2026
At ICST workshops today, giving a keynote on how test generation and dynamic analysis will boost AI agents: conf.researchr.org/details/ise-2026…
conf.researchr.org
The power of experimentation (Intelligent SE 2026) - Intelligent SE 2026
ISE Goals Many researchers utilize AI techniques. However, AI techniques, including deep learning techniques and LLMs, have probabilistic characteristics, so it is difficult to verify and validate AI-based software systems. In this regard, this workshop aims to discuss intelligent methods for verifying AI techniques in various aspects. This workshop encourages researchers to present interesting ideas and demonstrations in various aspects of safety, security, explainability, and fairness, as well as in domains such as autonomous flights and autonomous driving. Researchers can discuss how th ...
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 19/05/2026
Specification-based fuzzers are super-effective - but writing their formal specs needs lots of manual effort. Wednesday at 14:20, we show how to turn natural-language protocol specs (such as RFCs) into formal specs automatically - great perspectives for fuzzing! Details and paper […]
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 19/05/2026
Meet the #Fandango makers! If you're at #ICST26 and would like to see our language-based fuzzer in action, meet us in the tools and data showcase today at 14:00 and tomorrow at 10:30. Details and paper […]
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 19/05/2026
"Please produce an input that is (1) valid, (2) as short as possible, and (3) results in a maximum of code coverage." How can you tell a fuzzer to do this? Today 14:50 at #ICST26, see the latest extension of our #Fandango fuzzer. Details and paper […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 17/05/2026
On my way to Daejeon, South Korea for the #ICST conference, listening to a live football audio stream. Can you guess which one?
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 22/04/2026
I got interviewed by Nature on how to catch bugs in scientific software. My "Basics of Debugging 101" were: 1. Proceed systematically 2. Find out when the bug occurs 3. Explain the bug to a rubber duck 4. Write tests that replicate the bug Enjoy the read! […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 17/04/2026
This is the output I want. What input do I need? Today at ICSE - International Conference on Software Engineering, Tural Mammadov presented his work on Modelizer - the framework that learns from synthesized program executions to predict inputs from outputs […] [Original post on mastodon.social]
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 15/04/2026
I‘m gonna need a bigger suitcase #ICSE2026
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 14/04/2026
In the #ICSE2026 Wednesday 14:00 session, I will be giving my Harlan D. Mills Award talk (likely at 14:10 already). Enjoy! conf.researchr.org/details/icse-202…
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 10/04/2026
On my way to Rio de Janiero, visiting #ICSE2026 - here with Tural Mammadov. See you soon!
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 08/04/2026
Planning to visit #FSE2026 in Montreal? Do not miss our #Fandango tutorial on Sunday, July 5, where we show how to systematically generate inputs and interactions for comprehensive software testing (with José Antonio Zamudio Amaya, Marius Smytzek, and Alexander Liggesmeyer). Find Fandango at […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 19/03/2026
The #IEEE Computer Society interviewed me on my past and the Future of Automated #Debugging and Software #Testing Enjoy! www.computer.org/publications/tech-…
computer.org
The Future of Automated Debugging and Software Testing with Harlan D Mills Award Winner Andreas Zeller
Hardware-based protections validate what software cannot independently verify. They shift visibility from reactive observation to foundational assurance. This article takes a deeper look at the what, why, and how.An interview with Andreas Zeller, recipient of the 2026 IEEE Harlan D. Mills Award.
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 16/03/2026
For decades, my mission was to help developers build better software. Now I help anyone, including AI: andreas-zeller.info
Homepage of Andreas Zeller, now with the text "help build better software" rather than "help _developers_ build better software"
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 10/03/2026
In a call "retrieve(account: string)", nobody checks the contents of "account". What if we could specify its type not just as a string, but as a formal language - say, a regex "0-9]+"? In our new paper "FLAT: Formal Languages as Types" with Fengmin Zhu, we do […] [Original post on mastodon.social]
FLAT: Formal Languages as Types
And Their Applications in Testing
FENGMIN ZHU, CISPA Helmholtz Center for Information Security, Germany
ANDREAS ZELLER, CISPA Helmholtz Center for Information Security, Germany

Programmers regularly use strings to encode many types of data, such as Unix file paths, URLs, and email addresses. They are
conceptually different, but existing mainstream programming languages treat them as the same string type. This is problematic:
the type system allows, for instance, malicious HTML text to be passed to a function expecting an email address.
To distinguish conceptually different string types and to avoid potential vulnerabilities, we regard formal languages as types
(FLAT), thereby restricting the set of valid strings using context-free grammars and, if needed, semantic constraints. Applying
this type-based approach, we offer a unified solution for string API documentation, input validation, malicious input detection,
language-based fuzzing, and test oracles, all at once, based on user-annotated formal language types and, if necessary, pre-
and post-conditions. We implement this idea and present FLAT-PY, a testing framework for Python. By attaching annotations
directly to Python code, FLAT-PY automatically performs runtime type checking via code instrumentation and reports any
detected type errors as soon as possible...
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 09/03/2026
My successor as a professor will be some AI video tutor with the appearance of Brad Pitt, available 24/7, unlimited patience, personalized towards each student, the ability to teach any subject ever discussed in a textbook, and a cost of < 1$/hour. Good thing I can still do research! (Now wait...)
Brad Pitt in front of a classroom (AI-generated)
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 05/03/2026
"Should Computer Scientists Experiment Less?" This is the title of my upcoming Harlan D. Mills Award Talk at ICSE 2026 on the past, present, and future of Software Engineering research. Looking forward to lots of productive discussions! […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 04/03/2026
Impact award! I am happy to report that my ICSE 2006 paper "Mining metrics to predict component failures," with Nachi Nagappan and Thomas Ball, has been selected to receive a retrospective ICSE SEIP Most Influential Paper Award for its significant and lasting impact on the software engineering […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 03/03/2026
With more and more AI-generated code, comprehensive system testing becomes more important than ever. Our new paper "Language-Based Protocol Testing" (with Alexander Liggesmeyer and Pepe Zamudio), shows how to specify and test all details of how programs […] [Original post on mastodon.social]
Over the past decade, the automated generation of test inputs has made significant advances. Modern fuzzers and test generators easily
produce complex input formats that do systematically cover the input and execution space. Testing protocols, though, has remained a
frontier for automated testing, as a test generator has to interact with the program under test, producing messages that conform to
the current state of the system.
In this paper, we introduce language-based protocol testing, the first approach to specify, automatically test, and systematically cover
the full state and input space of protocol implementations. We specify protocols as interaction grammars—an extension of context-free
grammars that tag each message element with the communication party that is in charge of producing it. Interaction grammars embed
classical state models by unifying states, messages, and transitions all into nonterminals, and can be used for producing interactions as
well as parsing them, making them ideally suited for testing protocols. 
 By systematically
covering the interaction grammar and solving the associated constraints, FANDANGO achieves comprehensive coverage of the protocol
interactions, resulting in high code coverage and a thorough assessment of the program under test.
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 01/03/2026
On my way to Savannah, Georgia to an IFIP WG 4.3 meeting, where I’ll present our work on Parameterized Compiler Testing (a joint work with my fantastic co-workers Addison Crump and Alexi Turcotte)
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 26/02/2026
#Fandango 1.1 is now available! With this release, #Fandango becomes a full-fledged _protocol fuzzer_, happily exploring states and messages of protocols such as FTP or DNS. Thanks to José Antonio Zamudio Amaya. Valentin Huber, Alexander Liggesmeyer, and […] [Original post on mastodon.social]
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 13/02/2026
About time: A multi-celebration for becoming a member of Academia Europaea, my SIGSOFT Influential Educator Award, my 60th birthday, becoming an IEEE Fellow, _and_ getting the 2026 IEEE Harlan D. Mills Award. With cake and fizzy drinks!
Andreas Zeller and PhD students
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 10/02/2026
Starting this year, I will only review for conferences that get rid of a "bidding" phase, as allowing reviewers to bid on papers they want to review opens too many opportunities for manipulation and collusion. For details, see […]
mastodon.social
Original post on mastodon.social
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 05/02/2026
I am happy to report that I have been named the recipient of the 2026 Harlan D. Mills award "for sustained contributions to software debugging, program analysis, mining software repositories, and automated test generation." Let me thank my nominator Tom […] [Original post on mastodon.social]
Dear Prof. Zeller,
Upon recommendation of the IEEE Computer Society's Awards Committee and the approval of the society's Board of Governors, I am delighted to inform you have been selected to receive the
2026 Harlan D. Mills Award
«For sustained contributions to software debugging, program analysis, mining software repositories, and automated test generation."
The Harlan D. Mills Award recognizes researchers and practitioners who have demonstrated long-standing, sustained, and impactful contributions to software engineering practice and research through the development and application of sound theory. Further information about the award, including a list of past recipients, may be found at https://www.computer.org/volunteering/awards/mills
The award consists of a $3,000 honorarium, memento, and the invitation to give a talk during the
2026 International Conference on Software Engineering (ICSE), co-sponsored by IEEE Computer Society Technical Community on Software Engineering (TCSE). The conference will be held from 12 April through 18 April 2026 in Rio de Janeiro, Brazil. The conference coordinators will handle the award presentation arrangements.
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 03/02/2026
How do execution features relate to failures? In this new @ACM TOSEM paper, Marius Smytzek, Martin Eberlein, Lars Grunske, and I analyze which execution features beyond code coverage correlate best with failures and lead to accurate explanations of failure […] [Original post on mastodon.social]
Fault localization aims to identify code regions responsible for failures. Traditional techniques primarily correlate statement
execution with failures; however, program behavior involves diverse execution features, including variable values, branch
conditions, and definition-use pairs, which can provide richer diagnostic insights.
This paper comprehensively investigates execution features for fault understanding, addressing two complementary goals.
First, we conduct an empirical study of 310 bugs across 20 projects, analyzing 17 execution features and assessing their
correlation with failure outcomes. Our findings suggest that fault localization benefits from a broader range of execution
features: (1) Scalar pairs exhibit the strongest correlation with failures; (2) Beyond line executions, def-use pairs and functions
executed are key indicators for fault localization; and (3) Combining multiple features enhances effectiveness compared to
relying on individual features.
Second, building on these insights, we introduce a debugging approach that learns relevant features from labeled test
outcomes. The approach extracts fine-grained execution features and trains a decision tree to differentiate passing and failing
runs. The trained model generates fault diagnoses that explain the underlying causes of failures.
Our evaluation demonstrates that the generated diagnoses achieve high predictive accuracy. ...
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Andreas Zeller @andreaszeller.mastodon.social.ap.brid.gy · 30/01/2026
Four hours later, I _think_ I have fixed things again - reinstalled Python and all its packages, rebuilt Spotlight and Mail indexes, cleared macOS caches, subscribed to Creator Studio, and now back to these lost mails… Today I hate you, Apple.
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