/**
* Tests for calculation utilities
*/
import { describe, it, expect } from 'vitest';
import {
calculateFrenchPayment,
calculateTotalCost,
calculateTotalInterest,
generateLoanSummary,
} from '../../src/utils/calculations.js';
describe('calculateFrenchPayment', () => {
it('should calculate monthly payment correctly for standard loan', () => {
// $500,000 at 15% annual rate for 60 months
const payment = calculateFrenchPayment(500000, 15, 60);
// Expected ~11,895
expect(Math.round(payment)).toBe(11895);
});
it('should calculate monthly payment for high interest rate', () => {
// $100,000 at 30% annual rate for 24 months
const payment = calculateFrenchPayment(100000, 30, 24);
expect(Math.round(payment)).toBe(5591);
});
it('should handle zero interest rate', () => {
// $120,000 at 0% for 12 months = 10,000/month
const payment = calculateFrenchPayment(120000, 0, 12);
expect(payment).toBe(10000);
});
it('should calculate for short term loans', () => {
// $50,000 at 20% for 6 months
const payment = calculateFrenchPayment(50000, 20, 6);
expect(Math.round(payment)).toBe(8826);
});
it('should calculate for long term loans (mortgage)', () => {
// $1,000,000 at 8% for 240 months (20 years)
const payment = calculateFrenchPayment(1000000, 8, 240);
expect(Math.round(payment)).toBe(8364);
});
it('should return positive values for valid inputs', () => {
const payment = calculateFrenchPayment(100000, 10, 12);
expect(payment).toBeGreaterThan(0);
});
});
describe('calculateTotalCost', () => {
it('should calculate total loan cost correctly', () => {
const total = calculateTotalCost(10000, 12);
expect(total).toBe(120000);
});
it('should handle large payments', () => {
const total = calculateTotalCost(50000, 240);
expect(total).toBe(12000000);
});
it('should handle single payment', () => {
const total = calculateTotalCost(100000, 1);
expect(total).toBe(100000);
});
});
describe('calculateTotalInterest', () => {
it('should calculate total interest correctly', () => {
// Principal: 100,000, Monthly: 10,000, 12 months
// Total: 120,000, Interest: 20,000
const interest = calculateTotalInterest(100000, 10000, 12);
expect(interest).toBe(20000);
});
it('should return zero for zero interest loan', () => {
// Principal: 120,000, Monthly: 10,000, 12 months = no interest
const interest = calculateTotalInterest(120000, 10000, 12);
expect(interest).toBe(0);
});
it('should handle negative principal difference', () => {
// This shouldn't happen in practice, but tests edge case
const interest = calculateTotalInterest(50000, 1000, 12);
expect(interest).toBe(-38000);
});
});
describe('generateLoanSummary', () => {
it('should generate complete loan summary', () => {
const summary = generateLoanSummary(500000, 15, 60);
expect(summary).toHaveProperty('principal', 500000);
expect(summary).toHaveProperty('annualRate', 15);
expect(summary).toHaveProperty('termMonths', 60);
expect(summary).toHaveProperty('monthlyPayment');
expect(summary).toHaveProperty('totalAmount');
expect(summary).toHaveProperty('totalInterest');
expect(summary).toHaveProperty('currency', '$U');
});
it('should round payment values', () => {
const summary = generateLoanSummary(100000, 12, 24);
expect(Number.isInteger(summary.monthlyPayment)).toBe(true);
expect(Number.isInteger(summary.totalAmount)).toBe(true);
expect(Number.isInteger(summary.totalInterest)).toBe(true);
});
it('should calculate consistent values', () => {
const summary = generateLoanSummary(200000, 20, 36);
// totalAmount should be close to monthlyPayment * termMonths (within rounding tolerance)
const expectedTotal = summary.monthlyPayment * summary.termMonths;
expect(Math.abs(summary.totalAmount - expectedTotal)).toBeLessThanOrEqual(36); // 1 per month rounding tolerance
// totalInterest should equal totalAmount - principal
expect(summary.totalInterest).toBe(summary.totalAmount - summary.principal);
});
it('should handle edge case of 1 month term', () => {
const summary = generateLoanSummary(100000, 12, 1);
expect(summary.monthlyPayment).toBeGreaterThan(100000);
expect(summary.totalInterest).toBeGreaterThan(0);
});
});
