What are the primary differences between TDD and BDD? [closed]

Answer 1

It seems to me that BDD is a broader scope. It almost implies TDD is used, that BDD is the encompasing methodology that gathers the information and requirements for using, amongh other things, TDD practices to ensure rapid feedback.

Answer 2

Consider the primary benefit of TDD to be design. It should be called Test Driven Design. BDD is a subset of TDD, call it Behavior Driven Design.

Now consider a popular implementation of TDD - Unit Testing. The Units in Unit Testing are typically one bit of logic that is the smallest unit of work you can make.

When you put those Units together in a functional way to describe the desired Behavior to the machines, you need to understand the Behavior you are describing to the machine. Behavior Driven Design focuses on verifying the implementers' understanding of the Use Cases/Requirements/Whatever and verifies the implementation of each feature. BDD and TDD in general serves the important purpose of informing design and the second purpose of verifying the correctness of the implementation especially when it changes. BDD done right involves biz and dev (and qa), whereas Unit Testing (possibly incorrectly viewed as TDD rather than one type of TDD) is typically done in the dev silo.

I would add that BDD tests serve as living requirements.

Answer 3

To me primary difference between BDD and TDD is focus and wording. And words are important for communicating your intent.

TDD directs focus on testing. And since in "old waterfall world" tests come after implementation, then this mindset leads to wrong understanding and behaviour.

BDD directs focus on behaviour and specification, and so waterfall minds are distracted. So BDD is more easily understood as design practice and not as testing practice.

Answer 4

BDD is largely TDD done right. However, there's additional value that BDD offers. Here's a link on that:

BDD is more than “TDD done right”

Answer 5

I understand BDD to be more about specification than testing. It is linked to Domain Driven Design (don't you love these *DD acronyms?).

It is linked with a certain way to write user stories, including high-level tests. An example by Tom ten Thij:

Story: User logging in
  As a user
  I want to login with my details
  So that I can get access to the site

Scenario: User uses wrong password

  Given a username 'jdoe'
  And a password 'letmein'

  When the user logs in with username and password

  Then the login form should be shown again

(In his article, Tom goes on to directly execute this test specification in Ruby.)

The pope of BDD is Dan North. You'll find a great introduction in his Introducing BDD article.

You will find a comparison of BDD and TDD in this video. Also an opinion about BDD as "TDD done right" by Jeremy D. Miller

March 25, 2013 update

The video above has been missing for a while. Here is a recent one by Llewellyn Falco, BDD vs TDD (explained). I find his explanation clear and to the point.

Answer 6

With my latest knowledge in BDD when compared to TDD, BDD focuses on specifying what will happen next, whereas TDD focuses on setting up a set of conditions and then looking at the output.