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Code & Deliveryabbreviation · /ˌtiː diː ˈdiː/

TDD

TDD — Test-Driven Development is a software development practice where you write automated tests before writing the actual code that solves the problem.

In simple English

TDD is a fundamental methodology in modern software development that changes the traditional order of development. Instead of writing features and testing them afterward, developers using TDD follow this cycle: write a test that fails, write the minimum code to make it pass, then refactor. This approach helps catch bugs early, improves code quality, and creates comprehensive test coverage from the start. In practice, TDD is used extensively in Agile teams and is considered a best practice by many organizations. When a team practices TDD, new developers can refactor with confidence because the tests protect against breaking existing functionality. It also serves as living documentation because the tests show exactly how the code is supposed to behave. TDD requires discipline and experience to implement well. Teams must invest time upfront in writing tests, but this typically pays off through fewer production bugs, easier maintenance, and faster development cycles later.

How to say it: Spell it out: T-D-D ("tee-dee-dee").

Understand what Test-Driven Development is and how to apply it in software projects

At a glanceCEFR B2
Commonness5/5
Versatility4/5
FormalityCasualFormalNeutral
Spoken ↔ WrittenSpokenWrittenBoth
Directness ↔ DiplomaticDirectDiplomaticDirect
RegionUS and UK

Say it like this

  • We follow TDD principles on this project
  • Let's practice TDD for the new feature
  • TDD helps us maintain code quality

Use it at work

Process

  • We use TDD: write the test first, then the code.
  • Let's try TDD on this new module.

Explaining

  • With TDD, you go red, green, refactor.
  • TDD helps me design better APIs.

In an interview

  • Do you practice TDD?
  • How strict is TDD on your team?

Don't say this

✕We will test with TDD after we finish coding.
✓We will write tests first, then code using TDD.

TDD means writing tests BEFORE the code, not after. Writing tests after is called testing, not TDD.

Practice

Try it

4 quick exercises

Pick the most natural phrasing

1. Your team wants to improve code quality. Which statement sounds most natural?

Complete the sentence

2. We will _______ TDD for all new features starting next sprint.

Spot the mistake

3. Which sentence uses TDD incorrectly?

Rewrite naturally

4. Rewrite this sentence using TDD: 'We write tests after we finish the code to make sure it works.'

Say it out loud

Phrase 1 of 3

"We follow TDD principles on this project"

We don't save your recording. The word check uses your browser's speech recognition.

More about TDD

Real examples(3)

  • in a standup

    "Yesterday I wrote tests for the login feature using TDD before implementing the actual code."

  • in a code review

    "I notice you didn't follow TDD here. Can you add tests before we merge this?"

  • in a team meeting

    "If we adopt TDD company-wide, we should see a significant reduction in production bugs."

More mistakes(2)

Handle with care. TDD is sometimes confused with just testing code. It is specifically about writing tests first, before writing the feature code.

  • ✕TDD is just about testing your code.
    ✓TDD is a development methodology where tests drive the design and implementation.

    TDD is more than testing; it is a complete development approach that influences how you design and structure code.

  • ✕We do TDD by running our test suite once a week.
    ✓We practice TDD by writing a failing test, then writing code to pass it, then refactoring.

    TDD requires continuous, immediate feedback from tests as you code, not periodic testing.

Other forms(3)

  • TDD noun

    "TDD is an industry standard practice in many tech companies."

  • TDD practice noun

    "Our TDD practice has reduced bugs by 40 percent this quarter."

  • TDD-driven adjective

    "We use a TDD-driven approach to ensure high code quality."

Often used with(5)

  • practice TDD · means to use TDD methodology in your development process
  • follow TDD · means to adhere to TDD principles and workflows
  • adopt TDD · means to implement TDD as a team or organizational standard
  • TDD cycle · refers to the red-green-refactor workflow
  • TDD approach · means using TDD as a development strategy

Similar words(2)

  • test-first development · More explicit but less commonly used than TDD
  • test-driven design · Emphasizes the design aspect; TDD is more commonly used

Opposites(3)

  • ad hoc testing
  • manual testing
  • test-last approach

Questions(5)

What does TDD stand for?
TDD stands for Test-Driven Development. It is a software development methodology where developers write automated tests before writing the code that the tests verify.
What is the TDD cycle?
The TDD cycle is also called red-green-refactor. First, write a test that fails (red). Second, write minimal code to make the test pass (green). Third, improve the code without changing its behavior (refactor). Then repeat for the next feature or requirement.
Why is TDD important in software development?
TDD is important because it improves code quality, reduces bugs in production, makes refactoring safer, provides documentation through tests, and often leads to better software design. It also gives developers confidence when modifying code.
Is TDD used in real tech companies?
Yes, TDD is widely used in tech companies, especially those following Agile methodologies. Many companies like Google, Amazon, and Microsoft encourage or require TDD practices. However, adoption varies by team and project.
How do you use TDD in a sentence at work?
You can say: We practice TDD on this project. Let us follow TDD principles. We need to adopt TDD to improve quality. Can you write the test first using TDD?
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