When is refactoring a good decision?

625 words

2014-08-07 22:30

To develop working, valuable software, we expend time and decisions. In this context, a good decision is one which helps us deliver more value with our time. When might refactoring be a good decision?

What’s refactoring for?

I see refactoring, above all else, as a tool for managing risk.

Software development is naturally rich in risk. If we accept that it’s worth doing, then we’re accepting some amount of risk. For all but tiny projects, the greatest risks are likely:

  1. Making undesirable changes that go unnoticed until fixing them is surprisingly expensive
  2. Making desirable changes that seem worthwhile until implementing them proves surprisingly expensive

TDD can help us control (1) and — at no additional cost — affords us the option of refactoring, should we want to. And if we seek to control (2), I contend that we should want to.

Straw man: never stop refactoring!

Let’s say we not only put stories whose only purpose is refactoring on the backlog, but we’ve got lots and lots of “refactoring stories”, and we prioritize them over everything else. We’ll have maximized the number of possible future changes that are easy for us to make, but we’ll never get around to making any of them.

Straw man: never start refactoring!

Let’s say we not only don’t ask permission to refactor, we simply never refactor. We’ll have maximized how much time we’re working on changes motivated solely by business value, but we’ll have driven up two averages: the cost per change, and the risk of greatly underestimating the cost per change. Even if we accept that we’ve taunted Hofstadter’s Law.

Who decides to refactor?

Make it work (bee sinuously finding way to target flower), make it right, make it fast (bees making beelines for target flower)

Illustration by Rebekka Dohme.

I see developers bee-ing best positioned to decide whether, when, and how to refactor.

I don’t see that the “value” of refactoring and the “value” of software’s user-visible behavior can be measured along commensurate axes. The latter is what we’re here to do. The former is a way to improve our chances of doing it. The latter is best judged by the folks who rely on the outcome of what we make. The former is best judged by the folks who rely on the process of what we make.

When is refactoring a good decision?

If we agree that managing the risks of software development means mitigating its inherent variability while collecting just enough options along the way, then refactoring is likely a good decision when:

  • Developers choose it
  • Its intended scope is to clear a path in front of the desired change
  • Its intended effect is to deliver the desired change faster (or at least not much slower, and then to deliver future changes faster)

After some months of judicious and opportunistic refactoring (more or less depending on context), here are some trailing indicators that you’re reaping the benefits:

  • You rarely wish an estimate didn’t have to be so large
  • You almost never feel the need to fudge an estimate
  • You almost always get what you expected when you expected it


In software development, where risk management is a fact of life, refactoring is one of the most powerful tools at our disposal. Wielded wisely, it helps us more predictably deliver more value with our time.


My opinions generally derive from my experience (and, stubborn as I am, little else). The expression of this particular opinion is better for my having encountered the following expressions:

“If you want to estimate little things, you have to refactor.” — J. B. Rainsberger. 7 minutes, 26 seconds, and the Fundamental Theorem of Agile Software Development (Øredev 2013).

“Why refactor? Economics.” — Martin Fowler. Workflows of Refactoring (OOP 2014).

“Hofstadter’s Law: It always takes longer than you expect, even when you take into account Hofstadter’s Law.” — Douglas Hofstadter. Gödel, Escher, Bach (1979).

“Do not taunt Happy Fun Ball.” Saturday Night Live (1991).

Comments... [2]

One Russian soul

292 words

2014-06-29 17:09

Our hearts do in dark forests dwell.
Each feeling, choosing, kernel core
lives in a roughly-tangled dell,
a wilderness of soul and spore.

Each forest lives, each forest grows,
unfurls through time our destinies.
Alive with buzzing thoughts, each glows,
cohesive-seeming unities.

— Andrew Hamilton, “Akrasia Forest”

I’ve always wondered — sometimes more, sometimes less — what my life might become. Nine years ago those wonderings led me to the house and grave of my favorite composer. The past few months of leisurely introspection have encouraged me again to wonder more. When the past week found me within walking distance, I went for a return visit.

The tree where I sat, and Medtner's grave

I brought my changed self. Since Medtner’s resting place last observed me, I had not merely learned to play some and analyze some of his music, I’d finally composed some I was proud to call mine. On the off chance that wouldn’t suffice, I also brought flowers. Then I cued up my recorded performance of his Sonata-Reminiscenza, sat at the foot of an immense tree, and marveled at the life Medtner lived while making the music he made. Was the former a necessary precondition for the latter, or merely incidental? Are my preconditions likely similar to his? If I’m to write my music, what kind of life must I live? How can I be sure? How can I find out? The clouds parted. The birds resumed their song. I rose to my feet in appreciation.

No amount of wondering suffices to show me what my life will be. There’s only one way to find out. I hope, on my next visit, to play Medtner something wonderful and new. In the meanwhile, I know that my life is far better for his music, that it’s precious, and that it’s mine.

Никола́й Ме́тнер (

TDD in context #1: Keeping my job

807 words

2014-06-01 00:08

For a couple months now, I’ve been spoiling myself by spending the bulk of my time reducing my world’s entropy in three main ways:

1. Automate more of what I do
2. Organize more of what I know
3. Learn more of what I don’t know

I’ve begun exploring the boundaries of my attachment to Test-Driven Development. How did I get so attached in the first place? In large part, because the thinking process I’ve learned and applied by deliberately practicing TDD has, in the contexts I’ve experienced, almost always been an adaptive behavior. This is the first anecdote in a series about TDD’s value to humans.

My confidence

Claiming I do my job better with TDD is equivalent to claiming I do my job worse without it — which, last I checked, was true.

Shortly after graduating with my music degree, I was hired as a software developer in a highly regulated, tightly controlled corporate environment. The tools I was hired to develop had begun life as a proof-of-concept system to manage certain kinds of identities in a heterogeneous distributed network. They put it in production. It was a roaring success. Suddenly lots of customers appeared, wanting lots more use cases, business rules, and platforms added. Suddenly the security engineers realized their proof of concept had a long life ahead of it. It would need to be managed and developed as a software product.

They may have been confident in my fitness for the job, but I sure wasn’t. While I’d been a longtime contributor to some significant open-source projects, I hadn’t been a professional software developer since 2002. And that had been my first programming job. I’d learned a whole lot very quickly, including the rudiments of TDD and other XP practices, and I was probably worth what I’d gotten paid, but I had not, by any means, mastered much of anything.

My first assignment

To their credit, my superiors had devised for me a relatively gentle introductory exercise: when an identity is no longer needed, provide a way to “disable” it. I did not need to devise a mutually authenticated client and server that spoke a network protocol in order to manipulate the server’s database of identities by issuing commands to be processed or rejected according to business rules. I didn’t even need to tweak the database schema; it already contained the needed fields. I just needed to add a “disable” command. Reading through the “create” and “update” commands, I copy-paste-edited a new “disable” command. Then I figured out how to run my copy of the server, how to point my client at it, and how to prove to myself that my copy of the database correctly marked a given identity as disabled. (When I demonstrated my progress, I found out there was considerably more to it than that. A great deal of much-needed handholding occurred.)

Then it dawned on me: I bet a bunch of the other commands need to behave differently when asked to operate on an identity that’s been disabled, now that such things exist. Taking my best guesses at those behaviors, I edited the SQL backing those other commands until they probably handled both the old and new cases. Since I didn’t understand how most of the commands were intended to be used, let alone how to verify whether they worked, we code-reviewed my very simple changes. We agreed they looked fine.

My first deployment

Guess what happened when we put my code into production? That’s right: my new “disable” command worked, but users complained that several other commands no longer did. It was easy to spot the mistakes, now that we knew where they were, and to make the obvious fixes. We scrambled to redeploy.

Before I tell you how the postmortem went, remember the context:

1. The environment was highly regulated and tightly controlled
2. The code was security-sensitive
3. I’d been uncertain of my ability to do the job before screwing up in production

“Bill,” I said, because that was Bill’s name, “if you need me to avoid screwing up like that again…”

“Uh huh,” replied Bill.

“…then I need to be doing Test-Driven Development.”

“Listen,” said Bill. “Do whatever you think you need.”

I did. And over the several years that followed, I never screwed up like that again.

Before (code pouring all over the place) and after (code pouring cleanly through the TDD funnel)

Illustration by Rebekka Dohme.

My conclusion

You might suggest that that’s because I quickly learned the problem domain and our system’s model thereof, remembered how to write basic SQL, and made a habit of checking my assumptions and my results more carefully. You’d be right. You might suggest that I could have done all that without TDD. You’d be right again. But I’m fairly sure I did them sooner, better, and more reliably — all of which felt crucially important at the time — because of TDD.

As near as I can tell, TDD saved my job.

Comments... [2]

When I might not TDD

702 words

2014-05-09 00:16

Given a software project whose outcome and schedule truly matter, all other things being equal, I’d choose…

  • A capable team of TDD practitioners over another capable team
  • To have the team practice TDD

Of course, there are always a great many other things, and they be rarely equal. Let’s scale it down a bit.

Given the responsibility to deliver working, valuable software to humans, I’d choose to drive my development with tests. I believe I fulfill my responsibility faster and better when I do. This turns out to be one of my strongest and most deeply held beliefs of any kind, right up there with the intrinsic value of human beings and an overarching respect for individual autonomy.

Yeah, that sounds a little odd to me too. Yet my professional experiences have repeatedly borne out the validity and importance of all three.

Sticking with TDD here, I’ve read and/or conjectured lots of plausible mechanisms by which it could be speeding me up, I’ve observed a bunch of them directly, and anecdotally I’m usually pleasantly surprised how smoothly things go, compared to how I imagine they might have gone instead.

Software development isn’t a controlled experiment. It’s possible I’ve been continually and subtly lying to myself under the sway of a whole bunch of cognitive biases and thus I’ve been egregiously misinterpreting my personal anecdata.

Since “I do my job better when I practice TDD” is merely a strong belief, not a result that I’ve proven, I owe it to myself and the people I work with to question it from time to time. Inspired by some recent professional experiences, now is one of those times. Where are the boundaries of my belief? If I’m trying to be effective and efficient, when wouldn’t I practice TDD?

What I mean by TDD

TDD, to me, means holding a collaborative conversation with my code. I suggest what I think I want it to do next, ask it to try, listen to what it tells me, adjust my thinking and wanting, and repeat. To listen better and adjust faster, write smaller tests (in units of code, if inside-out; in slices of functionality, if outside-in).

If that metaphor doesn’t quite work for you, try this one: TDD means pair programming with myself. Before typing anything, I communicate my intent aloud. Maybe my pair has a better idea, or a question to consider, or a drawing board we should be going back to. By working in a way that externalizes my thinking, I can be my own pair.

Degenerate cases

I wouldn’t want TDD if…

  • It doesn’t need to work
  • It needs to work, but it doesn’t matter when
  • It’s so manifestly simple that it necessarily works
  • It won’t ever need to change
  • It’s so manifestly simple that it’ll be obvious how to change and necessarily still manifestly simple afterward
  • It’s a throwaway experiment to learn something
  • I’m being held at gunpoint by a crazed stakeholder who’ll shoot me if I write so much as a single test first (or try to have a conversation about it)

None of these cases is particularly interesting.

False negatives

You might think I wouldn’t want TDD if…

  • It’s legacy code
  • It’s otherwise hard to write tests for
  • Nobody else on the team bothers
  • I’m learning a new programming language
  • Unarmed stakeholders express opposition to it

You’d nearly always be wrong.

Learnings go here

I practice TDD for its many benefits. What if I could achieve those benefits another way?

As a useful oversimplification, the biggest external benefit of TDD might be that I get my work done faster and better, and the biggest internal benefit might be that I feel safer doing my work. (It seems plausible that there’s a causal relationship.) I’ve been working in a dynamic language famous for its runtime surprises, deriving a feeling of safety from my tests. Might there be a language where the compiler alone could give me that same feeling?

I can practice TDD because I’ve been targeting suitably unconstrained environments. Might there be a target whose constraints preclude TDD?

I don’t know for sure when I wouldn’t want TDD. But I’ve got some ideas, and watch out: I’m going to test them.

Shoulda bought yak insurance

410 words

2014-04-23 17:43

Hand-drawn yak with a safety razor going down its midsection

Illustration by Jason Crane.

My new Yak Shaving Expert t-shirt is fitting, and not only because it’s the right size. For instance, today I wanted to start backing up my email, so I found offlineimap to my taste, so I went to pkgsrc to install it and saw that we’re a couple releases behind, so I updated the package. Sometimes it turns out that in order to do what you want, it’s necessary that you first go shave a yak. Maybe I’ll get to try backing up my email tomorrow.

In software development, it’s pleasing when any desired change proves easy to make. When a change proves prohibitively difficult, we have to decide what to do: either to stop wanting it, or to want it anyway. In neither case will we be able to know the full cost of our decision. But our choice can and should be informed by our need for predictable cost of delivery in the future and our willingness to delay gratification in the present. It’s sort of like insurance. If over our product’s lifetime we need to minimize the frequency with which we have to stop everything and shave an entire yak, then we know the discipline required.

I’ve felt mildly and persistently overwhelmed since the great server crash of late 2008. First I had time to deal with the fallout, but no money; then money, but no time. Not having all my personal data organized and available has meant that for any given task, I’ve learned to assume I can’t just go and do it; instead, I’ll have to first figure out what I need, then go digging to find it all. Then, and only then, can I hope to complete the task. So the act of getting started has been harder than usual, the list of tasks has grown large, the cycle has been self-sustaining, and the effect of five years of this drip-drip-drip on my cognitive capacity has been noticeable, at least to me.

My personal yaks have finally come home to roost. (Yes, they’ve evolved the ability to roost.) I have money, time, grand ideas, and some clippers. Where to start? A few weeks ago I guessed I’d want to answer that only after refining my enormous backlog a bit. Now I think whichever item I feel like doing next is what I’ll do next. Why try to impose an ordering, when I know full well it’s yaks all the way down?

Older Posts