These aren't aspirations.
They're enforced on every project.

// This catches bugs at compile time, not in production interface CreateUserInput { email: string; role: 'admin' | 'user' | 'viewer'; organizationId: string; } // Zod validates at runtime boundaries const schema = z.object({ email: z.string().email(), role: z.enum(['admin', 'user', 'viewer']), organizationId: z.string().uuid(), });

// Test first, implement second describe('InvoiceService', () => { it('should calculate VAT correctly for EU clients', () => { const invoice = InvoiceService.create({ amount: 1000, clientCountry: 'DE', vatExempt: false, }); expect(invoice.vat).toBe(190); expect(invoice.total).toBe(1190); }); });

// Domain logic has zero framework dependencies // You can test this without a database or HTTP server class OrderService { constructor( private orderRepo: OrderRepository, private paymentGateway: PaymentGateway, private notifier: NotificationService, ) {} async placeOrder(input: PlaceOrderInput) { const order = Order.create(input); await this.paymentGateway.charge(order.total); await this.orderRepo.save(order); await this.notifier.send(order.confirmation); } }