Featured posts


A better way to reason about software testing terms

I was recently in a discussion between developers about improving the test coverage of a major software project. They needed guidance about what kind of tests to write, and how to write them.

The discussion quickly became confusing: the topic was too large, too general, and it turns out that there wasn't even a well-defined shared vocabulary for testing concepts! The latter turns out to be a wider problem in the software development community: it simply doesn't have well-defined testing terms!

In this post, I'd like to provide some guidance w.r.t. this matter. I'll discuss:

  • An overview of the most common testing terms.
  • A new way of reasoning about testing concepts: reiterating what actually matters, and categorizing tests based on "size" and "approach".
  • How the existing testing terminology fits in this new model.

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Debugging Docker builds

One of the projects I'm working on has a CI/CD pipeline that builds Docker images. The Dockerfile runs yarn install, then yarn build. The latter runs the TypeScript compiler tsc. Everything was working fine, but one day the build failed with the following error:

tsc: command not found

But TypeScript is still part of package.json. Nobody touched package.json or yarn.lock recently. Nobody could reproduce the problem locally with Docker: it only happened in the CI/CD pipeline. What is going on? We needed to debug the Docker build on the CI/CD server.

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What causes Ruby memory bloat?

Ruby apps can use a lot of memory. But why? Various people in the community attribute it to memory fragmentation, and provide two “hacky” solutions. Dissatisfied by the current explanations and provided solutions, I set out on a journey to discover the deeper truth and to find better solutions.

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Full-system dynamic tracing on Linux using eBPF and bpftrace

Linux has two well-known tracing tools:

  • strace allows you to see what system calls are being made.
  • ltrace allows you to see what dynamic library calls are being made.

Though useful, these tools are limited. What if you want to trace what happens inside a system call or library call? What if you want to do more than just logging calls, e.g. you want to compile statistics on certain behavior? What if you want to trace multiple processes and correlate data from multiple sources?

In 2019, there's finally a decent answer to that on Linux: bpftrace, based on eBPF technology. Bpftrace allows you to write small programs that execute whenever an event occurs.

This article shows you how to setup bpftrace and teaches you its basic usage. I'll also give an overview of how the tracing ecosystem looks like (e.g. "what's eBPF?") and how it came to be what it is today.

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How to build a good company purpose?

It has often been stated by business consultants and startup advisors that a company should have a purpose beyond vision. Studies show that that result in more motivated and loyal customers and employees. As Simon Sinek said: people don’t buy or follow what you do, but why you do it.

I agree. That was the easy part. But how do you actually define a good purpose? People need to feel that your purpose is aligned with their own values, and a purpose statement needs to balance many different things for many different people.

This post documents the start of my journey in an attempt to find answers.

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