software-design/refactoring-tidy-messy-code-without-breaking-it-using-tests-as-a-net.md

Refactoring: tidy messy code without breaking it, using tests as a net

Building software · 5 min read ·

Refactoring means changing how code is written without changing what it does, so the next person (often you) can read it. It sounds risky, and it is, unless you have a safety net.

Here you get a messy shipping cost function, eight tests, and a live editor. Tidy the code step by step and watch the tests stay green, then try a "harmless" edit that quietly breaks one rule and see exactly which test catches it.

Messy nested if statements turning into three flat lines of code, with 8 of 8 tests passing

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