What are the first tasks for implementing Unit Testing in Brownfield Applications?

Question

Do you refactor your SQL first? Your architecture? or your code base? Do you change languages? Do you throw everything away and start from scratch? [Not refactoring]

Answer 1

This really depends on the state of the codebase... are there massive classes? one class with mega-methods? Are the classes tightly coupled? is configuration a burden?

Considering this, I suggest reading Working Effectively with Legacy Code, picking out your problems, and applying the recommendations.

Answer 2

I'm adding unit testing to a large, legacy spaghetti codebase.

My approach is, when asked to solve a problem, I try to create a new wrapper around the part of the code-base which is relevant to my current task. This new wrapper is developed using TTD (writing the test first). Some of the time calling into the non-unit tested legacy code. At other times I make a new copy of an existing module and start to do serious violence to it. Sometimes I rewrite functionality from scratch.

But as I'm keeping it fairly well tested I feel pretty in control.

What I find with this code-base, which has been developed with far too much copy and pasting, is that once I get an understanding a particular part, and extract some functions from it (which are done test-first) ... these functions often turn out to be usable in many other places and so the rate of replacing the legacy code with my own, unit tested libraries increases.

I don't (and have no authority to) try to rewrite or add tests to parts of the code that are not touched by my current problem (usually a bug I'm trying to fix) but I do have a fairly aggressive proactive stance on anything that is touched and might be relevant.

Update : Penguinix asked : "What languages do you work in? Is there a specific Testing Harness you recommend?"

Right now I'm working in ... er ... Mumps! But the same principle works anywhere.

Something that transformed my understanding of UT was MinUnit : http://www.jera.com/techinfo/jtns/jtn002.html

When I saw MinUnit, that was kind of a "zen" moment of enlightenment for me. It stripped away the misunderstandings I had about unit testing being something complicated requiring sophisticated OO frameworks etc. I understood that UT was just about writing a bunch of tests. The "harness" you can write yourself, in about 3 minutes, in any language you like. Just get on and do it.