Relevant Mutants in a Flash

Relevant Mutants.

---

• Not all surviving mutants indicate weaknesses in tests.
• Not relevant surviving mutants (don’t signal any test weakness):

  • Ignore these ones:

    • In dead code (unreachable code)
    • In legacy seams (intentionally excluded from test execution).
    • Code not used because of legacy seams (also intentional).

  • Mutants in superfluous code:

    • They survive because the mutation did not change any behavior.
    • Still useful 💰: signal a possible simplification (refactoring opportunity).
• Relevant surviving mutants 💰: reveal genuine gaps in the test suite
  • e.g. missing boundaries, too lenient assertions, etc.
• Read Relevant Mutants.

Books I read (January - February 2026)

January
- The Fraud, Zadie Smith
- Son de Mar, Manuel Vicent
- Alien Clay, Adrian Tchaikovsky
- Misterios de Madrid, Antonio Muñoz Molina
- Simple Rules: How to Thrive in a Complex World, Donald Sull, Kathleen M. Eisenhardt
- The war of art, Steven Pressfield
- Solving the procrastination puzzle, Timothy A. Pychyl

February
- Ava en la noche, Manuel Vicent
- Dream Count, Chimamanda Ngozi Adichie
- Saturday night and Sunday morning, Alan Sillitoe
- Vibe Coding, Gene Kim, Steve Yegge

Interesting Talk: No Vibes Allowed: Solving Hard Problems in Complex Codebases

I've just watched this great talk by Dex Horthy

• No Vibes Allowed: Solving Hard Problems in Complex Codebases

Interesting Talk: From Vibe Coding To Vibe Engineering

I've just watched this funny talk by Kitze:

• From Vibe Coding To Vibe Engineering

Interesting Video: Does Code Quality Matter When AI Writes the Code?

I've just watched this interesting video by Tim Corey

• Does Code Quality Matter When AI Writes the Code?

Interesting Talk: Making Codebases Agent Ready

I've just watched this great talk by Eno Reyes

• Making Codebases Agent Ready

Interesting Talk: Can you prove AI ROI in Software Eng?

I've just watched this great talk by Yegor Denisov-Blanch

• Can you prove AI ROI in Software Eng? (Stanford 120k Devs Study)

This is a continuation of the study that appears in his previous talk: Does AI Actually Boost Developer Productivity? (100k Devs Study)

Interesting Talk: Using AI to Refactor Legacy Code: A Practical Guide

I've just watched this interesting talk by Scott Wierschem:

• Using AI to Refactor Legacy Code: A Practical Guide

Interesting Talk: Don’t get one-shotted: Use AI to test, review, merge, and deploy code

I've just watched this interesting talk by Tomas Reimers:

• Don’t get one-shotted: Use AI to test, review, merge, and deploy code

Interesting video: Claude Code is all you need in 2026

I've just watched this interesting video by Brian Casel

• Claude Code is all you need in 2026

Interesting Talk: Dispatch from the Future: building an AI-native Company

I've just watched this interesting talk by Dan Shipper:

• Dispatch from the Future: building an AI-native Company

Interesting Talk: Vibe coding and the evolution of developer experience tools

I've just watched this interesting talk by Harsha Shivanna:

• Vibe coding and the evolution of developer experience tools

Interesting Interview: Vibe Coding Solved What I Couldn't in 13 YEARS

I've just watched this great interview with Gene Kim on Tech Lead Journal channel

• Vibe Coding Solved What I Couldn't in 13 YEARS

Interesting Video: When to Vibe Code?

I've just watched this super interesting video by Graham Lee on a new dimension of technical debt in vibe-coded solutions:

• When to Vibe Code?

Interesting Talk: From autocomplete to agents: AI coding assistance state of play

I've just watched this interesting talk by Birgitta Böckeler

• From autocomplete to agents: AI coding assistance state of play

Interesting Talk: Automated software refactoring with OpenRewrite and OpenAI

I've just watched this interesting talk by Olga Kundzich and Sam Snyder

• Automated software refactoring with OpenRewrite and OpenAI

Interesting Talk: AI Hates Legacy Code

I've just watched this great talk by Ray Myers

• AI Hates Legacy Code

Interesting short conversation: How Agents Decide What to Use and When

I've just watched this great short conversation by Guy Podjarny and Simon Maple

• How Agents Decide What to Use and When

Interesting Talk: AI Coding: The State of The Mend

I've just watched this great talk by Ray Myers

• AI Coding: The State of The Mend

Interesting Video: Agents are Easy. REALLY : A Vibe Coding Journey

I've just watched this interesting video by Matt Maher

• Agents are Easy. REALLY : A Vibe Coding Journey

Interesting Talk: Self Coding Agents

I've just watched this great talk by Colin Flaherty

• Self Coding Agents

Interesting Talk: Playing the long game

I've just watched this great talk by Sheena O'Connell

• Playing the long game

Interesting Talk: Beyond Code: The Role of Developers in the Age of AI

I've just watched this great talk by Kesha Williams

• Beyond Code: The Role of Developers in the Age of AI

Interesting Talk: Making AI coding assistants better, even for your weird DSLs

I've just watched this great talk by George Fahmy

• Making AI coding assistants better, even for your weird DSLs

Interesting Talk: AI assisted programming: from inline completions to agentic workflows

I've just watched this great talk by Anton Arhipov

• AI assisted programming: from inline completions to agentic workflows

Interesting Talk: Large-scale refactors with Agents

I've just watched this great talk by Robert Brennan

• Large-scale refactors with Agents

Interesting Talk: Automating Large Scale Refactors with Parallel Agents

I've just watched this great talk by Robert Brennan

• Automating Large Scale Refactors with Parallel Agents

Interesting Talk: Beyond Tests What to Verify in AI Generated Code

I've just watched this great talk by Jennifer Sand and Brandy Pielech

• Beyond Tests What to Verify in AI Generated Code

Interesting Talk: Agent Skills, Rules, Subagents: Explained!

I've just watched this great short talk by Lee Robinson

• Agent Skills, Rules, Subagents: Explained!

Interesting Podcast: Don’t Trust AI Reporting! (Three Traps to Avoid)

I've just listened to this great podcast by Cal Newport

• Don’t Trust AI Reporting! (Three Traps to Avoid)

The discussion about AI Reporting traps occurs during the first 29 minutes of the podcast.

Interesting Talk: We Studied 150 Developers Using AI

I've just watched this interesting short talk by Dave Farley

• We Studied 150 Developers Using AI

Interesting Talk: How I Tamed Claude

I've just watched this interesting talk by Emmz Rendle

• How I Tamed Claude

Interesting Talk: Relax

I've just watched this interesting talk by Maximilian Schwarzmüller

• Spec-Driven Development in the Real World

Interesting Talk: "I shipped code I don't understand and I bet you have too"

I've just watched this interesting talk by Jake Nations

• "I shipped code I don't understand and I bet you have too"

Interesting Talk: The New Code

I've just watched this interesting talk by Sean Grove

• The New Code

Interesting Talk: ChatGPT & Copilot are NOT Refactoring Tools

I've just watched this interesting talk by Emily Bache

• ChatGPT & Copilot are NOT Refactoring Tools

Interesting Talk: Can Claude help with legacy code?

I've just watched this interesting talk by Alex Bolboaca

• Can Claude help with legacy code?

Interesting Talk: Augmented Coding: Mapping the Uncharted Territory

I've just watched this interesting talk by Lada Kesseler

• Augmented Coding: Mapping the Uncharted Territory

Books I read (January 2026)

January
- The Fraud, Zadie Smith
- Son de Mar, Manuel Vicent
- Alien Clay, Adrian Tchaikovsky
- Misterios de Madrid, Antonio Muñoz Molina
- Simple Rules: How to Thrive in a Complex World, Donald Sull, Kathleen M. Eisenhardt
- The war of art, Steven Pressfield
- Solving the procrastination puzzle, Timothy A. Pychyl

What I wrote in 2025

- A case of Shotgun Surgery (a translation and update of a previous post in Spanish coauthored with Fran Reyes).
- The class is not the unit in the London school style of TDD.
- Sprouting or wrapping?.
- Mutantes relevantes (a translation and update of a previous post in English).
- Integrando ApprovalsJS con WebStorm (coauthored with Fran Reyes).
- "Isolated" test means something very different to different people!.
- Usando conjuntamente ApprovalsJs y StrykerJS en WebStorm (coauthored with Fran Reyes).
- ¿Tamaño y nivel de detalle adecuados para una historia de usuario? (coauthored with Fran Reyes).
- Heuristics to determine unit boundaries: object peer stereotypes, detecting effects and FIRS-ness.
- Mejorar nuestros rojos (a translation and update of a previous post in English).
- Using prompt patterns to enhance how you learn about prompt patterns.
- Convirtiendo tests no paramétricos en paramétricos con la IA (e intentando generar ejemplos).
- Segregating a test builder applying the curiously recurring template pattern.
- Removing commented-out code (a translation and update of a previous post in Spanish coauthored with Fran Reyes).
- La clase no es la unidad en el estilo de TDD de Londres (a translation and update of a previous post in English).
- Nuestro flujo de decisión para refinar Historias de Usuario poco antes de empezar a desarrollarla (coauthored with Fran Reyes).
- Breaking out to improve cohesion (peer detection techniques).
- Refactoring the tests after a "Breaking Out" (peer detection techniques).
- Parallel change example: simplifying some test builders" (peer detection techniques).
- A simple example of the temporary field code smell.

Books I read 2025

January
- The three body problem, Liu Cixin
- Dark Forest, Liu Cixin
- Programming with Types, Vlad Riscutia
- Saturation point, Adrian Tchaikovsky
- Death's End, Liu Cixin

February
- One Day All This Will Be Yours, Adrian Tchaikovsky

March
- El invierno en Lisboa, Antonio Muñoz Molina
- Walking to Aldebaran, Adrian Tchaikovsky
- Interface-Oriented Design, Ken Pugh

April
- Elegant objects 2, Yegor Bugayenko
- Orbital, Samantha Harvey
- Song yet sung, James McBride
- Extreme Programming Applied: Playing to Win, Ken Auer, Roy W. Miller

May
- Extreme Programming Explored, William C. Wake
- Some desperate Glory, Emily Tesh
- Refactoring in large software projects, Stefan Roock, Martín Lippert
- Test-lists utilization in TDD: The role of test-lists in requirements traceability, Hassan Mahmood Khan, Ibrar Arshad (master thesis)
- The role of slicing in TDD, Dieste et al. (paper)
- Impact Mapping, Gojko Adzic

June
- Searching for Opportunities of Refactoring Sequences: Reducing the Search Space, Piveta et al. (paper)
- Be a Learning Machine, Alberto Souza
- GRASP and GOF Patterns in Solving Design Problems, R.M.Noorullah (paper)
- Raciones de diseño de software: Mini ensayos para developers, Fran Iglesias
- Test-Driven Development: A Practical Guide, Dave Astels
- Flexible, Reliable Software, Using Patterns and Agile Development, Henrik Bærbak Christensen
- The BDD Books - Discovery: Explore behaviour using examples, Gáspár Nagy, Seb Rose

July
- Pon tu código en forma con calistenia, Fran Iglesias
- Designing Object Systems: Object-oriented Modelling with Syntropy, Steve Cook, John Daniels
- How the Practice of TDD Influences Class Design in Object-Oriented Systems: Patterns of Unit Tests Feedback, Mauricio Aniche, Marco Aurelio Gerosa (paper)
- Taming your dragon: Addressing Your Technical Debt, Dr. Andrew Richard Brown

August
- Domain-Driven Refactoring: A hands-on DDD guide to transforming monoliths into modular systems and microservices, Alessandro Colla, Alberto Acerbis
- Through a mirror darkly: How programmers understand legacy code, Carlos L. Burgos, Julie J. C. H. Ryan, Edward Lile Murphree (paper)
- Software Archeology, Andy Hunt, Dave Thomas (article)
- AI-assisted Programming, Tom Taulli
- Sensemaking: What Makes Human Intelligence Essential in the Age of the Algorithm, Christian Madsbjerg
- Software Testing with Generative AI, Mark Winteringham
- Refactoring vs Refuctoring: Advancing the state of AI- automated Code improvements, Adam Tornhill, Markus Borg, Enys Mones (white paper)
- Leveraging Code Smell Detection with Inter-smell Relations, Błażej Pietrzak, Bartosz Walter (paper)

September
- When and why your Code starts to smell bad (paper), Michele Tufano et al.
- Stone and Sky, Ben Aaronovitch
- It can't happen here, Sinclair Lewis
- El código generado con IA necesita frenos, no acelerador (post), Jorge Castro
- Should we revisit Extreme Programming in the age of AI? (post), Jacob Clark
- Efective software design practices, Alberto Souza
- What is the point of learning to write in a world with AI? (post), Daisy Christodoulou
- Del capitalismo sin alternativa a la IA sin preguntas (post), Pau Samo
- Assuring good style for OO programs. Demeter Law (paper), Karl Lleberherr, Ian Holland

October
- Eyes on the code: Analyzing developers' responses during code snippet analysis (paper), Vinícius Martins et al
- Beltenebros, Antonio Muñoz Molina
- Tranvía a la Malvarrosa, Manuel Vicent
- The Pragmatic Programmer 20th anniversary edition, David Thomas, Andrew Hunt
- On Writing, Stephen King
- La gesta del marrano, Marcos Aguinis
- Thinking in Bets: Making Smarter Decisions When You Don't Have All the Facts, Annie Duke
- Test-Driven Development: Concepts, Taxonomy,and Future Direction (paper), David Janzen, Hossein Saiedian
- Balancing Coupling in Software Design: Universal Design Principles for Architecting Modular Software Systems, Vlad Khononov

November
- Beyond Vibe Coding, Addy Osmani
- Observability Engineering, Charity Majors, Liz Fong-Jones, George Miranda

December
- AI Engineering, Chip Huyen
- Java Design Patterns Workbook, Steve Metsker, William C. Wake
- ¡No pasarán!, Vittorio Giardino
- The Martian Contingency, Mary Robinette Kowal
- Kill it with fire, Marianne Bellotti
- Una historia particular, Manuel Vicent