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What is the difference between BDD and TDD?

Jim (James Paul) White
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Joined: May 28, 2006
Posts: 7
What is the difference between BDD and TDD?
Vish Shukla
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Joined: Oct 12, 2008
Posts: 111
BDD can be considered as a specialized case of TDD.

I am also learner of TDD & BDD. However, would like to share my understanding on this. Focus of BDD is more on the end to end behavior of the component or the system. Where in you involve business analyst/customer and developers. Hence, the language used in BDD is also more like natural language.

On the other end, focus of TDD is behavior of the unit under development, and general practice is to mock out the dependencies of the component. Which is more relevant for developers. The implication which I have experienced because of mocking is that one needs to know some level of implementation details of the component like dependencies of the component, what methods will be called in the dependent components (so you can mock out behavior of those methods). Which, in case of BDD, customer or business analyst doesn't really need to care about.

One could argue that people also write tests for components without mocking the dependencies when using TDD. My say on this would be if that component makes sense to business and covers business use-cases and was developed with "outside-in" approach, then it is indeed BDD.

Thanks & Regards,
Vishal Shukla


Thanks & Regards,
Vishal S Shukla (SCJP 93%, SCWCD 94%, SCBCD 100%)
Vish Shukla
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Joined: Oct 12, 2008
Posts: 111
John, it would be good to hear your words on this.
Burk Hufnagel
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Joined: Oct 01, 2001
Posts: 814
    
    3
Jim (James Paul) White wrote:What is the difference between BDD and TDD?


When I first learned about BDD, I thought it was strictly applied to entire programs or services. The diagram I had in my head was an extended version of the TDD process; for each specification, create unit tests and go through the Red/Green/Refactor process (see figure 1.7 in the sample chapter of BDD in Action) until the specified behavior is working properly, then take the next behavior and repeat.

You can also write lower level specifications for subsystems, so it scales down pretty well -- though it still feels odd to think about writing executable specifications for a single class. That doesn't mean it's wrong, just means I need to adjust my perspective a bit more. There's no reason not to write unit tests titled expect_Account_To_Lock_After_Three_Failed_Login_Attempts - in fact, for Java developers, using a name like that should help because they'll know it must be a test method since it's not strictly camel case.

OTOH, I don't think it's reasonable to try and scale TDD up to a program level. You'd have one test class with way too many methods.

That's my take on it, and I'm also interested in John's viewpoint.

Burk


SCJP, SCJD, SCEA 5 "Any sufficiently analyzed magic is indistinguishable from science!" Agatha Heterodyne (Girl Genius)
John Smart
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Joined: Aug 06, 2013
Posts: 33
    
    5
Yes, BDD works extremely well at both a requirements level (with tools like Cucumber and JBehave) and at a lower, more technical level. In face, BDD has its origins as an easier, more intuitive way to practice TDD. Specifications are specifications, no matter what the level - it's just that a high-level specification expressed in business terms helps communicate with stakeholders, where as a low-level specification for an individual class helps discover, describe and document your low-level APIs.
Burk Hufnagel
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Joined: Oct 01, 2001
Posts: 814
    
    3
John Smart wrote:Yes, BDD works extremely well at both a requirements level (with tools like Cucumber and JBehave) and at a lower, more technical level. In face, BDD has its origins as an easier, more intuitive way to practice TDD. Specifications are specifications, no matter what the level - it's just that a high-level specification expressed in business terms helps communicate with stakeholders, where as a low-level specification for an individual class helps discover, describe and document your low-level APIs.

I hadn't considered using something like Spock to write low level specifications instead of unit tests, but I think that might be a Great Idea.
Thank you for the insight,
Burk
 
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