Unit Testing in Fortran

Testing is central to modern software quality, yet many widely used Fortran codebases still lack automated tests. Existing tests are often limited to coarse end-to-end regression checks that provide only partial confidence. With the growth of open-source Fortran tools, we can now bring unit testing and continuous validation to legacy and modern Fortran projects alike.

This talk surveys the current landscape of Fortran testing frameworks before focusing on three I have evaluated in practice — pFUnit, test-drive and veggies — and explaining why pFUnit is often the most robust choice. I will discuss its JUnit-inspired design, use of the preprocessor, and the compiler idiosyncrasies that can still make adoption challenging. I will examine the hurdles that make testing Fortran hard: global state, oversized subroutines, legacy dependencies, and compiler-specific behaviour.

I will then present community-oriented efforts to improve testing practices in Fortran, including development of an open-source Carpentries-style training course on testing in Fortran, with plans to expand into a broader introduction to sustainable Fortran development using open-source linting and documentation tools such as Fortitude and Ford.

Attendees will gain practical guidance for introducing effective testing into existing Fortran codebases, and insight into current efforts towards modern workflows that support reproducibility and continuous delivery.