rqlite is a lightweight, open-source, distributed relational database built on SQLite and Raft. With its origins dating back to 2014, its design has always prioritized reliability, and quality. The robustness of rqlite is also a testament to its disciplined testing strategy: after more than 10 years of development and deployments, users have reported fewer than 10 instances of panics in production.
Testing a distributed system like rqlite is no small feat. It requires careful consideration of various layers: from individual components to the entire system in operation. Let’s explore how rqlite is tested, following its philosophy of maintaining quality without unnecessary complexity.
The Testing Pyramid: An Effective Approach
Testing rqlite adheres to the well-known testing pyramid, which prioritizes unit tests as the foundation, supported by integration tests, and capped with minimal end-to-end (E2E) tests. This strategy reflects decades of software development experience, ensuring test suites remain efficient, targeted, and easy to debug — and in my experience this approach works.
Unit Testing: The Core of Quality
At the base of the pyramid lies unit testing, covering isolated components. Unit testing dominates rqlite’s test suite because it offers the best balance of speed and precision. Given that rqlite’s database layer is built around SQLite, a “shared nothing” architecture, most database-related functionality can be reliably tested with unit tests.
Testing is a huge part of the design process. If a component cannot be unit-tested easily, it often signals issues with its design. A little dependency injection during testing is a good thing, but too much indicates an over-reliance on other components. And an emphasis on clean interfaces ensures that components remain focused on a single task.
As of version 8.34.0, the entire rqlite code base is approximately 75,000 lines long (including tests, but excluding imported packages). Of that rqlite’s unit test suite comprises 27,000 lines of source code, making it the largest testing investment. Despite its breadth, the entire suite runs in just a few minutes, enabling frequent testing durin
