Exactly my experience - I've done TDD for 3 different types of calculation functions in 3 different languages over the years, and all were beneficial: financial

Exactly my experience - I've done TDD for 3 different types of calculation functions in 3 different languages over the years, and all were beneficial: financial risk calculations in C++, report data calculations in PHP and billing calculations in JavaScript. On the other hand, TDD for operations that involve I/O (including user interactions) were not helpful at all.