Blaze—the variant of Bazel used internally at Google—was originally designed to build the Google monorepo. One of the beauties of sticking to a monorepo is code reuse, but this has the unfortunate side-effect of dependency bloat. As a result, Bazel and Blaze have evolved to support ever-increasingly-bigger pieces of software. The growth of the projects built by Bazel and Blaze has had the unsurprising consequence that our engineers all now have high-end workstations with access to massive amounts of distributed resources.
During the summer of last year, I hosted an intern who implemented sandboxfs: a FUSE-based file system that exposes an arbitrary view of the host’s file system under the mount point. At the end of his internship, we had a functional sandboxfs implementation and some draft patches for integration in Bazel. The goal of sandboxfs in the context of Bazel is to improve the performance of builds when action sandboxing is enabled.
This post is a short, generalized summary of the preceeding two. I believe those two posts put readers off due to their massive length and the fact that they were seemingly tied to Bazel and Java, thus failing to communicate the larger point I wanted to make. Let’s try to distill their key points here in a language- and project-agnostic manner.
In part 1 of this series, I made the case that you should run away from the shell when writing integration tests for your software and that you should embrace the primary language of your project to write those. Depending on the language you are using, doing this will mean significant more work upfront to lay out the foundations for your tests, but this work will pay off. You may also feel that the tests could be more verbose than if they were in shell, though that’s not necessarily the case.
My latest developer productivity rant thesis is that integration tests should be written in the exact same language as the thing they test. Specifically, not shell. This theory applies mostly to tests that verify infrastructure software like servers or command line tools. It is too easy to fall into the trap of using the shell because it feels like the natural choice to interact with tools. But I argue that this is a big mistake that hurts the long-term health of the project, and once trapped, it’s hard to escape.
As most programming languages with support for functions, the shell offers locally-scoped variables. Unfortunately, local variables are not the default. You must explicitly declare variables as local and you should be very strict about doing this to prevent subtle but hard-to-diagnose bugs. That’s it! What else is there to say about this trivial keyword? As it turns out, more than you might think.