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Asked: 2026-05-26T21:04:42+00:00

I am beginning to adopt Test Driven Design (TDD) behaviors and workflow for my

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I am beginning to adopt Test Driven Design (TDD) behaviors and workflow for my iOS development projects. There is at least one impediment though in the context of legacy software. I will often have to add features to a pre-existing code base that I am new to. I will typically want to refactor at the beginning of working with the code base which will often have no tests available to ensure that my refactor-ings are not altering code functionality or worse, adding bugs.

My question is how do TDD folks bootstrap the whole process when the code is not written from scratch but rather legacy code that they are brought in to work on?

Thanks,
Doug

UPDATE

For a concrete example, I am using the example from Martin Fowler’s Refactoring re-coded in Objective-C as a training device for TDD (and AppCode) >>

I built the code from tests. I found I needed to add instance variables to the Customer class to ensure I didn’t screw up the cost calculations in the statement method as I grew the code. This is the fundamental issue I need insight into.

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  1. Editorial Team

    To begin with, if you don’t understand the legacy code you’re working with, you need to fix that before you do things which you’re concerned may change behavior.

    In your situation, after understanding the legacy code, I would write tests that will run against that legacy code. Once you’re satisfied that these tests function as you expect, you’re in a much better position to test your refactored code to ensure it functions as the old code did.

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