test-driven-development

Test-Driven Development (TDD)

Comprehensive TDD patterns and practices for all programming languages. This skill eliminates ~500-800 lines of redundant testing guidance per agent.

When to Use

Apply TDD for:

• New feature implementation
• Bug fixes (test the bug first)
• Code refactoring (tests ensure behavior preservation)
• API development (test contracts)
• Complex business logic

TDD Workflow (Red-Green-Refactor)

1. Red Phase: Write Failing Test

Write a test that:
- Describes the desired behavior
- Fails for the right reason (not due to syntax errors)
- Is focused on a single behavior

2. Green Phase: Make It Pass

Write the minimum code to:
- Pass the test
- Not introduce regressions
- Follow existing patterns

3. Refactor Phase: Improve Code

While keeping tests green:
- Remove duplication
- Improve naming
- Simplify logic
- Extract functions/classes

Test Structure Patterns

Arrange-Act-Assert (AAA)

// Arrange: Set up test data and conditions
const user = createTestUser({ role: 'admin' });

// Act: Perform the action being tested
const result = await authenticateUser(user);

// Assert: Verify the outcome
expect(result.isAuthenticated).toBe(true);
expect(result.permissions).toContain('admin');

Given-When-Then (BDD Style)

Given: A user with admin privileges
When: They attempt to access protected resource
Then: Access is granted with appropriate permissions

Test Naming Conventions

Pattern: test_should_<expected_behavior>_when_<condition>

Examples:

• test_should_return_user_when_id_exists()
• test_should_raise_error_when_user_not_found()
• test_should_validate_email_format_when_creating_account()

Language-Specific Conventions

Python (pytest):

def test_should_calculate_total_when_items_added():
    # Arrange
    cart = ShoppingCart()
    cart.add_item(Item("Book", 10.00))
    cart.add_item(Item("Pen", 1.50))

    # Act
    total = cart.calculate_total()

    # Assert
    assert total == 11.50