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Test-Driven DevelopmentvsBehavior-Driven Development
What is the difference between TDD and BDD?
Updated 2 min read6 differences
In short
In TDD, developers write a failing test before the code that makes it pass, while BDD builds on it with plain-language scenarios the whole team can read.
Test-Driven Development
Test-driven development is a coding practice in which you write a failing test first, then write just enough code to pass it, and then clean up the design.
Read the page on Test-Driven DevelopmentBehavior-Driven Development
Behavior-driven development is a practice where developers, testers, and business people agree on plain-language examples that become automated tests.
Read the page on Behavior-Driven DevelopmentTest-Driven Development and Behavior-Driven Development compared
| Aspect | Test-Driven Development | Behavior-Driven Development |
|---|---|---|
| Focus | Correct, well-designed units of code | Behavior that users and the business expect |
| Written by | Developers | Developers, testers and product people together |
| Format | Test code in the project's programming language | Plain-language Given-When-Then scenarios |
| Typical level | Unit tests | Acceptance and feature-level tests |
| Starting point | A small failing test for the next bit of code | A conversation about examples of desired behavior |
| Main benefit | Better design and fast feedback for developers | Shared understanding of requirements across the team |
The difference, explained
Test-driven development (TDD) is a coding practice built on a short loop called red, green, refactor: write a small failing test, write just enough code to make it pass, then clean up. Behavior-driven development (BDD) grew out of TDD and focuses on how the system should behave from a user's point of view, often written as Given-When-Then scenarios.
The difference is audience and level. TDD is mainly a developer tool that shapes code design through unit tests written in a programming language. BDD is a collaboration practice: developers, testers and product people agree on concrete examples of behavior in plain language, and those scenarios become automated acceptance tests.
They fit together well. A team can write BDD scenarios to define what a feature must do, then use TDD at the code level to build the pieces that make those scenarios pass. BDD tools that use the Gherkin syntax link each plain-language step to a piece of test code.
A common misconception is that BDD simply means using a particular tool or writing tests with describe and it. The heart of BDD is the conversation that produces shared examples before coding starts; without it, Given-When-Then files are just wordier tests.
Which one should you use?
Choose Test-Driven Development when…
- You want tight feedback and better design at the code level.
- Requirements are technical, like a library or an algorithm.
- Mainly developers need to read the tests.
Choose Behavior-Driven Development when…
- Non-developers need to read and agree on the expected behavior.
- Requirements are often misunderstood between business and engineering.
- You want living documentation of how features should behave.
Readers ask
Is BDD better than TDD?
They solve different problems. TDD improves code design and gives developers fast feedback, while BDD improves shared understanding of requirements; many teams use both.
Can you do BDD without TDD?
Yes. You can write and automate behavior scenarios without writing unit tests first, although combining the two gives coverage at both the feature and the code level.
What does Given-When-Then mean?
It is a template for describing behavior: Given sets up the starting situation, When describes the action, and Then states the expected outcome.