Practicalities of Co-Locating Tests with Source Code

Key Takeaways

• Co‑locating tests puts them beside source files, eliminating navigation friction
• Mirrored test trees risk drift as source layout evolves
• Meson build can aggregate test files via a shared list
• Separate test runner directory keeps infrastructure isolated while sources stay together

Pulse Analysis

In embedded software development, test suites have traditionally lived in a parallel directory structure that mirrors the production code. While this separation offers a clean filesystem hierarchy and makes it trivial to exclude tests from builds, it also creates a hidden barrier. Engineers often have to switch contexts to locate or update tests, and over time the test tree can diverge from the source layout, leading to untested modules and increased maintenance overhead.

Co‑locating tests directly next to the source files addresses these pain points. By placing a *_test.c* file alongside its implementation, developers can instantly see the associated verification code, encouraging a test‑first mindset and reducing the "out of sight, out of mind" phenomenon. The proximity also cuts down on navigation time, allowing quicker iteration cycles—critical in resource‑constrained embedded environments where build times are already long. However, this convenience must be balanced with the need for distinct compilation flags, linker settings, and mock frameworks that differ from the production build.

The article’s Meson‑based solution offers a pragmatic compromise. Each module declares its production sources and appends its test files to a global list, which the top‑level build script later compiles into a dedicated test executable. This pattern preserves the modularity of the source tree while centralizing test infrastructure—such as harnesses, mocks, and runners—in a separate folder. The approach scales well with continuous integration pipelines, ensuring that every code change triggers comprehensive unit testing without polluting the main build artifacts. As more embedded teams adopt agile practices, co‑location paired with smart build orchestration becomes a compelling strategy for maintaining code quality and accelerating delivery.