Andreas Frömer, Head of Software Development at Finanztip, shared his success story of using TDD to rewrite a legacy application, to replace the old unmaintainable code with the new tested one.

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Andreas Frömer, Head of Software Development at Finanztip, successfully used TDD to rewrite a legacy application consisting of 3 million lines of code. Key lessons include starting with system level tests to avoid regression bugs and using feature flags to replace old code while retaining system behavior. The approach emphasizes starting with system level tests before moving to component tests and applying TDD for both rewriting and refactoring.

TDD - Rewriting 3 million lines of code

Lesson #2. Use feature flags to replace old code

3 million lines of code in 6 months?? 1 million removed, 2 million added… in 6 months… is NUTS!