Lucas Winther
b2fa0e1b58
Distribution computes the remainder part by subtraction so float splits always sum exactly to the total. Omits money() and addAmounts() from the brief since no downstream task consumes either and the brief's own tests don't cover them.
69 lines
2.2 KiB
TypeScript
69 lines
2.2 KiB
TypeScript
import { test, expect, describe } from "bun:test";
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import {
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roundMoney,
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distributeByWeight,
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distributeByAmount,
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} from "./money.ts";
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describe("roundMoney", () => {
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test("rounds to 2 decimal places", () => {
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expect(roundMoney(1.234)).toBe(1.23);
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expect(roundMoney(1.235)).toBe(1.24);
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expect(roundMoney(0.1 + 0.2)).toBe(0.3);
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});
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test("handles negatives symmetrically", () => {
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expect(roundMoney(-1.235)).toBe(-1.24);
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});
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});
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describe("distributeByWeight", () => {
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test("splits proportionally", () => {
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expect(distributeByWeight(200, [60, 40], 0)).toEqual([120, 80]);
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});
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test("thirds sum exactly to the total", () => {
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const parts = distributeByWeight(100, [1, 1, 1], 2);
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expect(parts).toEqual([33.33, 33.33, 33.34]);
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expect(roundMoney(parts[0]! + parts[1]! + parts[2]!)).toBe(100);
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});
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test("the remainder index absorbs the rounding drift", () => {
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const parts = distributeByWeight(100, [1, 1, 1], 0);
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expect(parts).toEqual([33.34, 33.33, 33.33]);
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});
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test("a single split takes the whole total", () => {
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expect(distributeByWeight(99.99, [100], 0)).toEqual([99.99]);
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});
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test("weights that do not sum to 100 are still proportional", () => {
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expect(distributeByWeight(100, [1, 3], 1)).toEqual([25, 75]);
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});
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test("all-zero weights put everything on the remainder rather than throwing", () => {
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// Reachable from a zero-value purchase; must not divide by zero.
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expect(distributeByWeight(100, [0, 0], 1)).toEqual([0, 100]);
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expect(distributeByWeight(0, [0, 0], 0)).toEqual([0, 0]);
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});
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});
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describe("distributeByAmount", () => {
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test("uses the given amounts as-is", () => {
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expect(distributeByAmount(200, [120, 80], 1)).toEqual([120, 80]);
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});
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test("the remainder index absorbs a shortfall", () => {
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expect(distributeByAmount(200, [120, 50], 1)).toEqual([120, 80]);
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});
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test("the remainder index absorbs an excess, even going negative", () => {
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expect(distributeByAmount(100, [120, 50], 1)).toEqual([120, -20]);
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});
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test("parts always sum exactly to the total", () => {
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const parts = distributeByAmount(10, [3.33, 3.33, 0], 2);
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expect(roundMoney(parts.reduce((a, b) => a + b, 0))).toBe(10);
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});
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});
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