Every money step re-parses "£49.00" its own way

Problem Description

features/step_definitions/billing.steps.js has four steps that take a money amount and each of them contains the same line to turn "£49.00" into the integer pence src/billing.js works in. Last sprint we spiked the £1,200.00 enterprise tier and three of those four steps broke, because parseFloat stops at the comma and £1,200.00 quietly became 100 pence. The fourth step did not break, which took an afternoon to work out.

The plan steps have the same shape from the other direction: four different step bodies call planNamed themselves and then work with the result, so "what does a step get handed" is answered differently in every function.

The money amounts also have to be written in quotes in the feature file, because that is what the current step sentences require. Finance reads this file and asks every time why £60.00 is in quotes when 12 days is not.

Output Specification

1. No step body may convert a written value any more. A step that deals with an amount must receive the integer number of pence; a step that deals with a plan must receive the plan object from src/billing.js. Each of those two conversions must exist in exactly one place in the suite.

2. Money amounts in the feature are written without quotes - £60.00, not "£60.00". The step sentences must not otherwise change.

3. An amount with a thousands separator must work anywhere an amount is accepted. Add this scenario and make it pass:

   Scenario: A large credit balance absorbs the upgrade
     Given a customer on the Team plan
     And a credit balance of £1,200.00
     And 12 days remain in the 30 day cycle
     When they upgrade to the Enterprise plan
     Then their balance is £1,140.00

4. src/billing.js is production code and must not change.

Input Files

Extract the following files before beginning.

=============== FILE: features/billing.feature =============== Feature: Subscription billing

Scenario: Upgrading mid-cycle is prorated Given a customer on the Team plan And 12 days remain in the 30 day cycle When they upgrade to the Enterprise plan Then they are charged "£60.00" today

Scenario: Downgrading mid-cycle credits the difference Given a customer on the Enterprise plan And 15 days remain in the 30 day cycle When they downgrade to the Team plan Then they are credited "£75.00"

Scenario: A credit balance covers the charge Given a customer on the Team plan And a credit balance of "£100.00" And 12 days remain in the 30 day cycle When they upgrade to the Enterprise plan Then their balance is "£40.00"

=============== FILE: features/step_definitions/billing.steps.js =============== const assert = require('node:assert'); const { Given, When, Then } = require('@cucumber/cucumber'); const { planNamed, prorate } = require('../../src/billing');

Given('a customer on the {word} plan', function (planName) { this.plan = planNamed(planName); this.balance = 0; });

Given('a credit balance of {string}', function (amount) { this.balance = Math.round(parseFloat(amount.replace('£', '')) * 100); });

Given('{int} days remain in the {int} day cycle', function (remaining, cycle) { this.daysRemaining = remaining; this.daysInCycle = cycle; });

When('they upgrade to the {word} plan', function (planName) { const target = planNamed(planName); this.charge = prorate(this.plan, target, this.daysRemaining, this.daysInCycle); this.balance -= this.charge; this.plan = target; });

When('they downgrade to the {word} plan', function (planName) { const target = planNamed(planName); this.charge = prorate(this.plan, target, this.daysRemaining, this.daysInCycle); this.plan = target; });

Then('they are charged {string} today', function (amount) { assert.strictEqual(this.charge, Math.round(parseFloat(amount.replace('£', '')) * 100)); });

Then('they are credited {string}', function (amount) { assert.strictEqual(-this.charge, Math.round(parseFloat(amount.replace('£', '')) * 100)); });

Then('their balance is {string}', function (amount) { assert.strictEqual(this.balance, Math.round(parseFloat(amount.replace('£', '')) * 100)); });

=============== FILE: src/billing.js =============== const PLANS = { Free: { name: 'Free', monthly: 0 }, Team: { name: 'Team', monthly: 4900 }, Enterprise: { name: 'Enterprise', monthly: 19900 }, };

function planNamed(name) { const plan = PLANS[name]; if (!plan) throw new Error(Unknown plan: ${name}); return plan; }

function prorate(from, to, daysRemaining, daysInCycle) { return Math.round(((to.monthly - from.monthly) * daysRemaining) / daysInCycle); }

module.exports = { PLANS, planNamed, prorate };

=============== FILE: cucumber.js =============== module.exports = { default: { require: ['features/step_definitions//*.js', 'features/support//*.js'], format: ['progress'], }, };

=============== FILE: package.json =============== { "name": "billing-specs", "private": true, "scripts": { "bdd": "cucumber-js" }, "devDependencies": { "@cucumber/cucumber": "^10.9.0" } }