Bad Behavior (Driven Development) + CHEAT SHEET

This is a cash machine. Otherwise know as an ATM.

I must have used one of these things a thousand times.

And the process is always the same.

So when I came to do an episode on Behaviour Driven Development - BDD - and did the “classic” ATM example, how did I manage to screw it up?

Corrigendum

And this is my first ever video erratum.

And yes, I did have to look it up.

And when I did I found an even more interesting word:

Corrigendum

So welcome to this corregendum.

A few months ago I did a video on BDD - Behaviour Driven Development. And I used an example of a cash machine. You might know it as a an ATM.

Truth be told, this was laziness on my part.

Introducing BDD

This is Dan North.

He’s the guy that coined the term Behaviour Driven Development.

And, presumably, the abbreviation BDD.

(Please don’t make the mistake of calling it an acronym. It’s not an acronym.)

And this is the post that kicked it off “Introducing BDD”.

And way way down the page is an example of what Dan refers to as “the classic example of an ATM machine”.

Given the account is in credit
  And the card is valid
  And the dispenser contains cash
When the customer requests cash
Then ensure the account is debited
  And ensure cash is dispensed
  And ensure the card is returned

The version that appeared in my video was suspiciously similar:

Given the account balance it £100
  And the card is valid
  And the machine contains enough money
When the Account Holder requests £20
  Then the Cashpoint should dispense £20
  And the account balance should be $80
  And the card should be returned

And you know what?

It was months before anyone pointed out that the sequence of events… isn’t quite right.

//Missing text

I should say that since then, several of you have made the same observation.

Errors everywhere

Then I hit a problem: it wasn't as easy to fix as I'd hoped.

No problem, I thought: I’ll just Google it.

I discovered something interesting: Dan North’s classic example is all over the web.

I hunted through page after page…

The exact same example each time.

Attempt One

It seemed I would be forced to engage brain after all.

This was my first attempt:

Given the account is in credit
  And the card is valid
  And the dispenser contains cash
When the customer requests cash
Then the card is returned
When the customer withdraws the card    
Then the account is debited
  And cash is dispensed
  And the card is returned

It's a bit messy. Not sure there is a

Given > When > Then > When > Then

structure in bdd!

Attempt Two

Then I wondered if there were two scenarios:

Given the account is in credit
  And the card is valid
  And the dispenser contains cash
When the customer requests cash
Then the card is returned

And the second:

Given that (lots of good stuff has happened)
 When   customer withdraws the card 
Then the account is debited
  And cash is dispensed

Hmm. That feels like two incomplete scenarios. What I need is something that’s… whole.

Attempt Three

How about this:

Given the account is in credit
  And the card is valid
  And the dispenser contains cash
When the customer requests cash
  And the card is returned
  And the customer withdraws the card   
Then the account is debited
  And cash is dispensed

What do reckon?

Is that it?

Let me know in the comments here

The TDD vs BDD Cheat Sheet

If you haven't done so already, now would be a great time to grab this rather lovely cheat sheet

The TDD vs BDD cheat sheet.