test-driven-development

🔴🟢♻️ Test-Driven Development (TDD)

Philosophy: Red -> Green -> Refactor. Write failing tests first, make them pass, then improve.

Workflow

1. 🔴 Red (Write Failing Test)

• Before writing any implementation code, create a test file.
• Write a test that describes the expected behavior.
• Run the test. It MUST fail. If it passes, the test is wrong.

2. 🟢 Green (Make it Pass)

• Write the minimum code required to make the test pass.
• Do not over-engineer. Do not add features not yet tested.
• Run the test. It MUST pass.

3. ♻️ Refactor (Improve the Code)

• Clean up the implementation. Remove duplication. Improve naming.
• Run the test again. It MUST still pass.
• Commit your work.

Examples

Backend (pytest):

# 1. Red - Write test first
def test_calculate_discount_applies_percentage(self):
    result = calculate_discount(100, 0.1)
    assert result == 90  # This will fail initially

# 2. Green - Minimal implementation
def calculate_discount(price, percentage):
    return price * (1 - percentage)

# 3. Refactor - Improve if needed

Frontend (Testing Library):

// 1. Red
test('clicking delete removes item from list', async () => {
  render(<ItemList items={mockItems} />);
  await user.click(screen.getByRole('button', { version: 0.1.0
name: /delete/i }));
  expect(screen.queryByText(mockItems[0].name)).not.toBeInTheDocument();
});

Benefits of TDD

• Forces you to think about API before implementation.
• Builds a safety net for future refactoring.
• Documentation through tests.

Guidelines

• One test = one concept. Don't test multiple behaviors in one test.
• Tests should be independent and runnable in any order.
• Treat test code with the same respect as production code.