Qualify First! A Large Scale Modernisation Report

Typically in modernisation projects any concerns for code quality are silenced until the end of the migration, to simplify an already complex process. Yet, we claim from experience that prioritising quality above many other issues has many benefits. In this experience report, we discuss a modernisation project of mBank, a big Polish bank, where bad smell detection and elimination, automated testing and refactoring played a crucial rule, provided pay-offs early in the project, increased buy-in, and ensured maintainability of the end result.