What TDD is

TDD is a workflow:

1. write a failing test (Red)
2. write minimal code to pass (Green)
3. refactor safely (Refactor)

Diagram: red-green-refactor

  graph LR
A[Red\nFailing test] --> B[Green\nMake it pass]
B --> C[Refactor\nImprove design]
C --> A

Why TDD helps

• forces clarity on requirements
• encourages smaller functions
• reduces fear of refactoring

Realistic TDD

TDD is easiest for:

• pure functions
• business rules

Harder for:

• UI code
• code with many external integrations

In those cases, combine TDD with integration tests.

🧪 Try It Yourself

Exercise 1 – Write a unittest TestCase

Exercise 2 – assertRaises

Exercise 3 – setUp and tearDown