How Antithesis Found and Explained a Bombadil Race Condition
Disclosure: I’m the original author and lead for the Bombadil project at Antithesis.
Oskar Wickström
Software design, testing, functional programming, and other delightful things.
Latest posts
Coding on Paper
About three months ago, I bought the Onyx BOOX 25.3” Mira Pro Color, an e-ink monitor for desktop use. I’ve used it as my primary monitor since, and I’ve had a lot of questions about it. This is my experience report, from the perspective of a working, still mostly typing, programmer.
Catching Typos on My Website with Browser Testing
One neat thing about Bombadil’s specification language is that it’s plain TypeScript, with access to external NPM packages. I’ve written a specification that spell-checks my website — what you’re reading now — and I want to share how that turned out.
The Bombadil Terminal Experiment
Last week at Bug Bash 2026, I had a bunch of interesting discussions about testing non-web interfaces with Bombadil, our new property-based testing framework for user interfaces. One direction that I already wanted to explore is terminal user interfaces (TUIs), and the hallway discussions gave me a nudge to get going. I started hacking on the flight back home, and a few days later that embryo of a…
There and Back Again: From Quickstrom to Bombadil
Today I’m announcing and open-sourcing the Bombadil project — a brand new property-based browser testing framework. I started working on this when joining Antithesis two months ago. While still in its infancy, we’ve decided to build it in the open and share our progress from the start.
Computer Says No: Error Reporting for LTL
Quickstrom is a property-based testing tool for web applications, using QuickLTL for specifying the intended behavior. QuickLTL is a linear temporal logic (LTL) over finite traces, especially suited for testing. As with many other logic systems, when a formula evaluates to false — like when a counterexample to a safety property is found or a liveness property cannot be shown to hold — the computer…
Programming in the Sun: A Year with the Daylight Computer
I’ve been hinting on X/Twitter about my use of the Daylight DC-1 as a programming environment, and after about a year of use, it’s time to write about it in longer form. This isn’t a full product review, but rather an experience report on coding in sunlight. It’s also about the Boox Tab Ultra – which has a different type of display – and how it compares to the DC-1 for my use cases.
Finding Bugs in a Coding Agent with Lightweight DST
Amp is a coding agent which I’ve been working on the last six months at Sourcegraph. And in the last couple of weeks, I’ve been building a testing rig inspired by Deterministic Simulation Testing (DST) to test the most crucial parts of the system. DST is closely related to fuzzing and property-based testing.
Machine: Learning; Human: Unlearning;
This last month has been fascinating. I guess LLMs have finally resonated with me on a deeper level. It wasn’t like I woke up and suddenly everything was different, but their impact is growing on me non-linearly, forcing me to rewire my brain.
How I Built "The Monospace Web"
Recently, I published The Monospace Web, a minimalist design exploration. It all started with this innocent post, yearning for a simpler web. Perhaps too typewriter-nostalgic, but it was an interesting starting point. After some hacking and sharing early screenshots, @noteed asked for grid alignment, and down the rabbit hole I went.
A Flexible Minimalist Neovim for 2024
In the eternal search of a better text editor, I’ve recently gone back to Neovim. I’ve taken the time to configure it myself, with as few plugins and other cruft as possible. My goal is a minimalist editing experience, tailored for exactly those tasks that I do regularly, and nothing more. In this post, I’ll give a brief tour of my setup and its motivations.
Statically Typed Functional Programming with Python 3.12
Lately I’ve been messing around with Python 3.12, discovering new features around typing and pattern matching. Combined with dataclasses, they provide support for a style of programming that I’ve employed in Kotlin and Typescript at work. That style in turn is based on what I’d do in OCaml or Haskell, like modelling data with algebraic data types. However, the more advanced concepts from Haskell —…
Specifying State Machines with Temporal Logic
Quickstrom uses linear temporal logic (LTL) for specifying web applications. When explaining how it works, I’ve found that the basics of LTL are intuitive to newcomers. On the other hand, it’s not obvious how to specify real-world systems using LTL. That’s why I’m sharing some of my learnings and ideas from the past year in the form of blog posts.
The First Winter: Clearing Weeds and Planting Trees
In October 2020, we got our new house. Built 2013, it’s not only new to us, and this is a major upside. While I definitely can appreciate many aspects of old houses, the comfort of a modern house fits us first-time parents very well.
Introducing Quickstrom: High-confidence browser testing
In the last post I shared the results from testing TodoMVC implementations using WebCheck. The project has since been renamed Quickstrom (thank you, Tom) and is now released as open source.
The TodoMVC Showdown: Testing with WebCheck
In this post I’ll share the results from testing TodoMVC implementations using my new testing tool named WebCheck. I’ll explain how the specification works, what problems were found in the TodoMVC implementations, and what this means for my project.
Time Travelling and Fixing Bugs with Property-Based Testing
Property-based testing (PBT) is a powerful testing technique that helps us find edge cases and bugs in our software. A challenge in applying PBT in practice is coming up with useful properties. This tutorial is based on a simple but realistic system under test (SUT), aiming to show some ways you can test and find bugs in such logic using PBT. It covers refactoring, dealing with non-determinism,…
Property-Based Testing in a Screencast Editor, Case Study 3: Integration Testing
In the last article we looked at how Komposition automatically classifies moving and still segments in imported video media, how I went from ineffective testing by eye to finding curious bugs using property-based testing (PBT). If you haven’t read it, or its preceding posts, I encourage you to check them out first:
Property-Based Testing in a Screencast Editor, Case Study 2: Video Scene Classification
In the previous case study on property-based testing (PBT) in Komposition we looked at timeline flattening. This post covers the video classifier, how it was tested before, and the bugs I found when I wrote property tests for it.
Property-Based Testing in a Screencast Editor, Case Study 1: Timeline Flattening
In the first post of this series I introduced the Komposition screencast editor, and briefly explained the fundamentals of property-based testing (PBT). Furthermore, I covered how to write testable code, regardless of how you check your code with automated tests. Lastly, I highlighted some difficulties in using properties to perform component and integration testing.
Property-Based Testing in a Screencast Editor: Introduction
This is the first in a series of posts about using property-based testing (PBT) within Komposition, a screencast editor that I’ve been working on during the last year. It introduces PBT and highlights some challenges in testing properties of an application like Komposition.
Why I'm No Longer Taking Donations
Haskell at Work, the screencast focused on Haskell in practice, is approaching its one year birthday. Today, I decided to stop taking donations through Patreon due to the negative stress I’ve been experiencing.
Writing a Screencast Video Editor in Haskell
For the last six months I’ve been working on a screencast video editor called Komposition, and it’s now released and open source. This is an experience report, based on a talk from Lambda World Cádiz 2018, that’ll give an overview of Komposition’s design, implementation, testing, and planned future work.
Declarative GTK+ Programming with Haskell
This post introduces a declarative GTK+ architecture for Haskell which I’ve been working on during the journey with FastCut, a video editor specialized for my own screencast editing workflow. It outlines the motivation, introduces the packages and their uses, and highlights parts of the implementation.
Finite-State Machines, Part 2: Explicit Typed State Transitions
In the first part of this series, we left off having made states explicit using Haskell data types. We concluded that state transitions were implicit, and that a mistake in implementation, making an erroneous state transition, would not be caught by the type system. We also noted that side effects performed at state transitions complicated testing of the state machine, as we were tied to IO.
Finite-State Machines, Part 1: Modeling with Haskell Data Types
Stateful programs often become complex beasts as they grow. Program state incohesively spread across a bunch of variables, spuriously guarded by even more variables, is what I refer to as implicit state. When working with such code, we have to reconstruct a model mentally, identifying possible states and transitions between them, to modify the program with confidence. Even if a test suite can…
Motor: Finite-State Machines in Haskell
While writing my talk “Finite-state machines? Your compiler wants in!”, I have worked on porting the Idris ST library to Haskell. I call it Motor.
Automating the Build of your Technical Presentation
Writing technical presentations that include code samples and diagrams can be really tedious. In mainstream presentation software, such as Keynote and PowerPoint, your workflow is likely to manually copy-and-paste source code from your editor into your slides. If you’re not using the drawing capabilities of your presentation software, you have to perform similar steps to include diagrams.
Tagless Final Encoding of a Test Language
I have experimented with a test language encoded in tagless final style, instead of algebraic data types, to support the typed combinators beforeEach and beforeAll. Although the intended use is for PureScript Spec, I want to share the Haskell prototype I ended up with, and explain how I got there.
Hyper: Elegant Weapons for a More Civilized Page
Since laying Oden aside, I have been getting back into PureScript, and started working on a project called Hyper that I would like to introduce you to.
Taking a Step Back from Oden
I have decided to stop working on Oden.
Custom Formatting in HTML and LaTeX Code Listings using Pandoc
I have worked intensively on the Oden User Guide lately, primarily on improving content, but also on providing high-quality PDF and HTML output formats with detailed control over typesetting.
Paramount Color Scheme for Vim
Having tried a lot of color schemes for editors, especially for Vim, I have gotten quite picky. All right, very picky. Most of the time Vim has been configured to use Tomorrow Night or Gruvbox. Although they’re great, they have felt a bit over the top. Also, depending on where I’m sitting at the moment I use both dark and light backgrounds for best contrast.