Object Mentor Blog: The Truth about BDD

The Truth about BDD

Uncle Bob — Thu, 27 Nov 2008 16:25:38 -0600

I really like the concept of BDD (Behavior Driven Development). I think Dan North is brilliant, and had done us all a great service by presenting the concept.

OK, you can “feel” the “but” coming, can’t you?

It’s not so much a “but” as an “aha!”. (The punch line is at the end of this article, so don’t give up in the middle.)

BDD is a variation on TDD. Whereas in TDD we drive the development of a module by “first” stating the requirements as unit tests, in BDD we drive that development by first stating the requirements as, well, requirements. The form of those requirements is fairly rigid, allowing them to be interpreted by a tool that can execute them in a manner that is similar to unit tests.

For example,

  GIVEN an employee named Bob making $12 per hour.
  WHEN Bob works 40 hours in one week;
  THEN Bob will be paid $480 on Friday evening.

The Given/When/Then convention is central to the notion of BDD. It connects the human concept of cause and effect, to the software concept of input/process/output. With enough formality, a tool can be (and has been) written that interprets the intent of the requirement and then drives the system under test (SUT) to ensure that the requirement works as stated.

The argued benefit is that the language you use affects the way you think (See this. and so if you use a language closer to the way humans think about problems, you’ll get better thought processes and therefore better results.

To say this differently, the Given/When/Then convention stimulates better thought processes than the AssertEquals(expected, actual); convention.

But enough of the overview. This isn’t what I wanted to talk about. What struck me the other day was this…

The Given/When/Then syntax of BDD seemed eerily familiar when I first heard about it several years ago. It’s been tickling at the back of my brain since then. Something about that triplet was trying to resonate with something else in my brain.

Then yesterday I realized that Given/When/Then is very similar to If/And/Then; a convention that I have used for the last 20+ years to read state transition tables.

Consider my old standard state transition table: The Subway Turnstile:

Current State	Event	New State	Action
LOCKED	COIN	UNLOCKED	Unlock
LOCKED	PASS	LOCKED	Alarm
UNLOCKED	COIN	UNLOCKED	Thankyou
UNLOCKED	PASS	LOCKED	Lock

I read this as a set of If/And/Then sentences as follows:

If we are in the LOCKED state, and we get a COIN event, then we go to the UNLOCKED state, and we invoke the Unlock action.
If we are in the LOCKED state, and we get a PASS event, then we stay in the UNLOCKED state, and we invoke the Alarm action.
etc.

This strange similarity caused me to realize that GIVEN/WHEN/THEN is simply a state transition, and that BDD is really just a way to describe a finite state machine. Clearly “GIVEN” is the current state of the system to be explored. “WHEN” describes an event or stimulus to that system. “THEN” describes the resulting state of the system. GIVEN/WHEN/THEN is nothing more than a description of a state transition, and the sum of all the GIVEN/WHEN/THEN statement is nothing more than a Finite State Machine.

Perhaps if I rephrase this you might see why I think this is a bit more than a ho-hum.

Some of the brightest minds in our industry, people like Dan North, Dave Astels, David Chelimsky, Aslak Hellesoy, and a host of others, have been pursuing the notion that if we use a better language to describe automated requirements, we will improve the way we think about those requirements, and therefore write better requirements. The better language that they have chosen and used for the last several years uses the Given/When/Then form which, as we have seen, is a description of a finite state machine. And so it all comes back to Turing. It all comes back to marks on a tape. We’ve decided that the best way to describe the requirements of a system is to describe it as a turing machine.

OK, perhaps I overdid the irony there. Clearly we don’t need to resort to marks on a tape. But still there is a grand irony in all this. The massive churning of neurons struggling with this problem over years and decades have reconnected the circle to the thoughts of that brave pioneer from the 1940s.

But enough of irony. Is this useful? I think it may be. You see, one of the great benefits of describing a problem as a Finite State Machine (FSM) is that you can complete the logic of the problem. That is, if you can enumerate the states and the events, then you know that the number of paths through the system is no larger than S * E. Or, rather, there are no more than S*E transitions from one state to another. More importantly, enumerating them is simply a matter of creating a transition for every combination of state and event.

One of the more persistent problems in BDD (and TDD for that matter) is knowing when you are done. That is, how do you know that you have written enough scenarios (tests). Perhaps there is some condition that you have forgotten to explore, some pathway through the system that you have not described.

This problem is precisely the kind of problem that FSMs are very good at resolving. If you can enumerate the states, and events, then you know the number of paths though the system. So if Given/When/Then statements are truly nothing more than state transitios, all we need to do is enumerate the number of GIVENs and the number of WHENs. The number of scenarios will simply be the product of the two.

To my knowledge, (which is clearly inadequate) this is not something we’ve ever tried before at the level of a business requirements document. But even if we have, the BDD mindset may make it easier to apply. Indeed, if we can formally enumerate all the Givens and Whens, then a tool could determine whether our requirements document has executed every path, and could find those paths that we had missed.

So, in conclusion, TDD has led us on an interesting path. TDD was adopted as a way to help us phrase low level requirements and drive the development of software based on those requirements. BDD, a variation of TDD, was created to help us think better about higher level requirements, and drive the development of systems using a language better than unit tests. But BDD is really a variation of Finite State Machine specifications, and FSMs can be shown, mathematically, to be complete. Therefore, we may have a way to conclusively demonstrate that our requirements are complete and consistent. (Apologies to Godel).

In the end, the BDDers may have been right that language improves the way we think about things. Certainly in my silly case, it was the language of BDD that resonated with the language of FSM.

"The Truth about BDD" by ????????? PDF

Sun, 15 Jan 2012 19:50:23 -0600

????? PDF Based on the same conversion engine, both our free online service and Nitro Pro desktop tool. ????? PDF ? DOC make converting PDF to Word easy with Nitro Pro taking you to a new level in speed, accuracy, and control. ????? PDF ? PPT Use Nitro Pro to batch convert large collections of files with just a few clicks ????? PDF ? Word Microsoft Word, Excel, and more. And, its intuitive tools make editing text and images directly within PDF files easier than ever before.

"The Truth about BDD" by backup iphone sms

Wed, 11 Jan 2012 05:38:09 -0600

Take effect to save the file and you can retrieve them when necessary.

"The Truth about BDD" by fashion wool caps.

Tue, 03 Jan 2012 18:57:14 -0600

DC Shoes Caps| http://www.capsroom.com/special-caps-dc-shoes-caps-c-125_175.html Top Caps| http://www.capsroom.com/special-caps-top-caps-c-125_157.html Fashion Wool Caps| http://www.capsroom.com/brand-caps-fashion-wool-caps-c-124_141.html

"The Truth about BDD" by mulberry bags

Tue, 03 Jan 2012 18:53:31 -0600

mulberry bags store http://www.bestmulberryhandbags.com mulberry bags sales http://www.bestmulberryhandbags.com mulberry bags sales online http://www.bestmulberryhandbags.com

"The Truth about BDD" by mulberry bags

Tue, 03 Jan 2012 18:52:35 -0600

Mulberry bag specializes in natural leather items, on the Mulberrycheap mulberry bags sale plant is found south-west of The uk tradesmen to make superb, pairing useful, primary plus leather effect and authentic inventive style and design and delightful model avoid various other manufacturers, to help classic classic design, everything thick and also formidable smell while in the synthetic leather, extensive by using steel rivets,replica mulberry handbags and harness, the previous copper-colored material pieces, it cannot support although consider middle age periods around The eu, simple, naive tiny aspiration a kind of fortification along with knights in battle, the vast majority of awful occasions grade will not conveniently copy the actual icon. When specific awareness of the fabric, therefore the identical portion of the program in various household leather development, demonstrating your flavoring won’t be the same, much like the Congo incredible leather-based, tough Scotchgrain leather, in addition to high-quality Indian He handwear cover natural leather, reliability of study course, irrespective of beginning, but another coloring, anyone can obtain the most suited for their color, almost like tailor-made standard, lots of stylish people is to resist it is beauty.Michael Hundred Li (Mulberry) United kingdom experienced on the last century, and many cultural store model, has become to the trough,discount mulberry handbags but because Two thousand, following the procedure of the latest expense, enable Meters 250 Li (Mulberry) brand of quick alteration, much more throughout November 2004, earned a “British Design Council” (English Manner Authority) presented a “best Gadgets layout Award” (Most effective Accessory Designer 2004), the emblem is a large beneficial. M 250 Li (Mulberry) brand name by means of more radiant, additional pouches, additional buckles, extra rivets,mulberry purse sale combined with the elegance and also practicality of your design, yet again swept the planet.

"The Truth about BDD" by miu miu authentic handbags

Tue, 03 Jan 2012 01:16:25 -0600

miu miu authentic handbags | http://www.bestmiumiuhandbags.com best miu miu replica handbags | http://www.bestmiumiuhandbags.com cheap replica miu miu handbags | http://www.bestmiumiuhandbags.com miu miu fake handbags | http://www.bestmiumiuhandbags.com

"The Truth about BDD" by fitted 59fifty cap

Thu, 29 Dec 2011 02:18:48 -0600

In addition, based on the fitted 59FIFTY choose the best side very first. One of the main square face type (condition), the spherical encounter (round face), which the actual (surface area) that three.Round encounter, the face is a big domehttp://www.capsroom.com/baseball-caps-boston-red-sox-c-121_136.html '> baseball cap rack caps, hats, small. Should you put on the limit width is much more suitable. Tips to encounter using the first little, but additionally show the following big thin face. Consequently, wearing a dome limit is much more appropriate. All nations face the individual putting on the cap of the kind suitable.Then according to their determine, choose a cap. Figure flattery should be adequately large not small, light or large sense of cephalopods. The actual determine is the reverse smaller. Women put on high hats polohttp://www.capsroom.com/baseball-caps-c-121.html '>59fifty baseball caps Chandler, otherwise do not give a person “and” greater feeling. Microsoft. Short on behalf of a new period of toned broad-brimmed<a href=’ http://www.capsroom.com/baseball-caps-chicago-white-sox-c-121_129.html ‘>59fifty custom hats cap, and not apt to be more brief prominence. Wearing a cap and outfitting the same, want to try to foster strengths and bypass weaknesses, as well as with fulfillment, so that people checked out the elegant. Forms and colors of caps, clothes, must scarves, mitts as well as shoes along with other facilities. Ladies wear eyeglasses, don’t put it on having a advanced decorative at wholesale prices cap, the actual hat darkish astringenhttp://www.capsroom.com/baseball-caps-chicago-white-sox-c-121_129.html '> fitted 59fifty cap t adverse brow, hat is higher, which could show you the way and the natural as well as unrestrained elegance.

"The Truth about BDD" by graduate school personal statement

Fri, 23 Dec 2011 08:14:45 -0600

Very good to read your most informative article. Its very informative and well written also.

"The Truth about BDD" by The Beats Headphones

Mon, 05 Dec 2011 00:49:52 -0600

beats headphones review
beats headphones on sale
beats headphones cheap

Beats headphones on sale
Beats headphones cheap
beats headphones tour

Beats Studio By Dr. Dre
Best Studio Headphones
Studio Headphones Reviews

dr dre beats review
dr dre beats cheap
dr dre beats outlet

dr dre beats online shop
dr dre beats cheap
dr dre beats wholesale
ykwyy-clj1205

"The Truth about BDD" by http://www.cheaphatscaps.org

Fri, 02 Dec 2011 00:33:10 -0600

Over 2000 styles of cheap hats and fitted caps are choices you should nevermisss. Pick up your favorite cheap fitted hats , Red bull and cheap snapback hats today.

"The Truth about BDD" by Cheap Beats By Dre

Tue, 15 Nov 2011 01:40:05 -0600

bus today, make them Cheap Beats By Dremiserable. One said: “I ??am really unlucky it! I was packed Beats By Dre Studioin the car to flow production.” One said: “I ??called Beats By Dre Soloit bad luck! In I was packed car are pregnant.Beats By Dre Pro Classic joke: I TVU A university studentbeats by dr dre caught by the enemy, the enemy tied him at the poles,just beats solo headphones purple and then asked him: say, where are you? You do not say it electrocuted! Scheap dr.dre beats studio headphones balck/yellowtudents back to the enemy a word, the result was electrocuted, he said: I am TVU.Hot sale beats by dr dre pro headphones

"The Truth about BDD" by beats by dre Australia

Sun, 13 Nov 2011 21:01:48 -0600

This is a very good article, I like it very much, I hope you write more articles!

"The Truth about BDD" by http://www.asicschuhe.com/

Fri, 11 Nov 2011 19:12:30 -0600

Asics Schuhe ist die beste Laufschuhe,Beste Verarbeitungen, hochwertige Materialen und ein unverwechselbares Design machen Asics Schuhe zum Liebhaber vieler Schuhfans, denn sie sind auch für den Alltag perfekt Asics Schuhe!

"The Truth about BDD" by filipino hats

Fri, 11 Nov 2011 01:36:30 -0600

I am so glad this internet thing works and your article really helped me. Might take you up on that home advice you.

"The Truth about BDD" by fake gucci belt

Thu, 03 Nov 2011 22:12:52 -0500

advantages, the biggest advantage,fake gucci belt the price is cheap, bright red color diversity, design DuoZhong diversity (in China’s main origin for wenzhou of zhejiang and yiwu). B, weakness, fake gucci belt

"The Truth about BDD" by christian louboutin

Mon, 31 Oct 2011 07:57:10 -0500

Great post, please write more about this, and I like it. I really enjoy reading your blog popular distributed: a good article waiting for you! Greate post,please write more about this,and I like it,I really enjoy reading you blog popular distributed: a good article waiting for you!

"The Truth about BDD" by casque dr dre

Mon, 31 Oct 2011 03:53:57 -0500

casque dr dre cher casque beats by dre beats casque distributors casque beats by dre online beats by dr dre casque

nouveau style dr dre beats cher nouveau arriver dr dre beats beats by dr dre spiderman casque casque spiderman beats by dre

beats by dr dre superman casque superman beats by dre casque

casque chrome colorware casque beats by dre chrome colorware

beats by dr dre beats by dre sale cheap beats by dre beats by dre store high quality headphones new design headphones discount beats by dre cheap beats by dre beats by dre canada monster beats by dre free shipping dr dre beats monster beats online

"The Truth about BDD" by betty

Sat, 29 Oct 2011 01:48:07 -0500

Control everything of your life.

"The Truth about BDD" by lily8901

Sat, 29 Oct 2011 01:46:34 -0500

Good good study,day day up.

"The Truth about BDD" by moncelrtzmart

Fri, 28 Oct 2011 02:26:01 -0500

Faux fur leather jackets and suede leather jackets are common. To know about the exact material usedMonclerfor manufacturing faux leather jackets and suede leather jackets you must understand what this faux fur and suede is. Moncler VestesAs is known leather is obtained from animal skin. Firstly the skin is removed from animal’s body.

"The Truth about BDD" by virtual blackjack reviews

Thu, 20 Oct 2011 03:52:29 -0500

This is very much virtual blackjack reviews enjoyed the great info is visible in this blog that to using the great services in this blog. I am very much satisfied by the BREAKING VEGAS CASINO great info is visible in this blog that to utilize the great services in this blog. This info is really useful info in this website GOLDEN VIP CLUB CASINO This is really like it very much for providing the great services in this blog CASINO NIGHT TIME Thanks a lot for providing the great info is visible in this blog.

"The Truth about BDD" by casque dr dre

Sun, 16 Oct 2011 20:31:15 -0500

casque dr dre cher casque beats by dre beats casque distributors casque beats by dre online beats by dr dre casque

nouveau style dr dre beats cher nouveau arriver dr dre beats beats by dr dre spiderman casque casque spiderman beats by dre

beats by dr dre superman casque superman beats by dre casque

casque chrome colorware casque beats by dre chrome colorware

Cheap Beats By Dre Dr Dre Headphones Cheap Monster Beats Headphones Beats By Dr Dre

New Style Beats By Dre Headphones

Cheap Dr Dre Studio Headphones Beats By Dre Studio

Cheap Dr Dre Pro Headphones Beats By Dre Pro

Cheap Dr Dre Solo Headphones Beats By Dre Solo

beats by dr dre beats by dre sale cheap beats by dre beats by dre store high quality headphones new design headphones

cheap beats by dr.dre studio limited edition-colorful champagne cheap beats by dr.dre colorful champagne

"The Truth about BDD" by Ashley Bowling

Sun, 16 Oct 2011 01:48:05 -0500

A good beginning makes a good ending A good man is hard to find A house divided against itself cannot stand

"The Truth about BDD" by cheap tisa snapbacks

Thu, 13 Oct 2011 01:16:57 -0500

This can be a significant issue. No matter which prospect America chooses this kind of The fall of will certainly earn besides the ability to rul the land, he’ll almost certainly have got our prime freedom regarding losing the primary message if your 2010 softball time of year commences.Presumably,discount designer handbag your following chief executive may have this available funds for an real measured 59fifty limit, instead of the deal model proven right here. I aquired the actual cover in a Wal-Mart within August 2005 if your Countrywide League enhanced to include the Nats.I’m delighted how the franchise’s cut back this vintage program ???W using a crimson cap,gucci scarf the same as this model worn out because of the Buenos aires Senators with this junior.Those people had been this hapless Senators 2.Zero, this team this had become the Colorado Ranger. The initial Senators bolted the actual Section involving The philipines well before plus took over as the Mn Twin babies.I’ve truly looked for the net carefully regarding pictures with McCain in addition to Barak dressed in cheap tisa snapback hats, and that i ended up being pleasantly surprised to seek out somewhat couple of. I ran across photographs involving Government wearing any Ma Reddish Sox as well as hat, however, not much else. The fresh York Moments reviews that Ruben McCain usually wears shelves to guard the epidermis with the sunlight, but the image with all the narrative demonstrated them dressed in precisely what usually any cap with the American banner.

"The Truth about BDD" by cheap tisa snapbacks

Thu, 13 Oct 2011 01:15:30 -0500

The particular trail abbreviation complete Testosterone levels plus Versus?¡ì?Cthe unique abbreviation in touch with Prizefighter Vuitton, super stars as well as method Monogrammed which includes quaternity petals and leaves are specifically hence thundering which a very careful routine maintenance could possibly be impacted. What exactly on the planet is usually author, ???bogus best Louis Vuitton handbag?has now recognized right into the spectacular design meaning together with LV is unquestionably often favourite furthermore closest by simply those who’re personal overconfident, gracious or possibly go on. Brought by simply skill film maker, Marc Medical doctor, the newest variety of Lv answers has achieved success fast and even obtains ideal accolade within internationally.As a thus excellent prepare, Prizefighter Vuitton things are subject matter to get luxurious goods.cheap tisa snapbacks About this, many people purchase to express during which Gladiator Vuitton items will be values despite the fact that authentic due to its excessive grade.Honies makes us notice fortuitous, cosy in addition to easeful. The truth is, the majority of us move while in the existen your current really enjoy,Gucci Men Wallets suitable? At the same time husband or wife, getting has to be felt slow and punctiliously, thus may perhaps Louis Vuitton.