Technical debt is like gaining weight. You rarely notice when it happens. No single shortcut causes the problem. But over time, seemingly simple changes take forever and break things you didn't touch. Your development slows down and you don't know why.
The cure is refactoring — small, safe, incremental improvements backed by tests. Not a rewrite. Not a big bang cleanup sprint. Just steady, disciplined improvement of the code you already have.
This course teaches you how to recognise code that needs improvement and how to improve it without breaking anything.
Day 1 — The four rules of simple design
Kent Beck defined four rules, in order of importance: tests pass, reveal intent, no duplication, keep it small. Simple to state. Surprisingly hard to follow consistently.
You will work through exercises that challenge your sense of what “simple” means. You will learn why naming and structure matter more than cleverness. You will practise the DRY principle — not just avoiding duplicated code, but duplicated concepts and structures. You will apply the Single Responsibility Principle to methods, classes, and modules until every piece of code has one reason to exist and one reason to change.
And you will learn why rule one comes first. Without tests, refactoring is gambling. With tests, refactoring is safe.
Day 2 — Refactoring in practice
Day two is about doing it. You will take real code with real smells — long methods, mixed abstraction levels, hidden duplication — and improve it step by step. Every step backed by a test. Every step small enough to revert if something goes wrong.
You will learn to recognise the most common code smells and apply refactoring patterns: extract method, introduce parameter object, replace conditional with polymorphism, and more. You will practise until the rhythm of small, safe improvements becomes second nature.
You will also learn when to stop. Not every piece of code needs to be perfect. The goal is code that is good enough to change safely and understand quickly — not code that wins a beauty contest.
What you bring home
The ability to look at code and see what needs to change. The discipline to change it safely. And the habit of leaving code better than you found it — one small step at a time.