git.scottworley.com Git - inverse-tax/blob - tax.test.js

   1 "use strict";
   2
   3 var assert = require('assert');
   4
   5 function test(description, f) {
   6   f();
   7 }
   8
   9 function rand(limit = 99) {
  10   return Math.round(Math.random() * limit);
  11 }
  12
  13 function make_random_tax_table() {
  14   function make_random_table(min_threshold) {
  15     if (rand(4) == 0) return [];
  16     const start = min_threshold === undefined ? rand() : min_threshold;
  17     const end = start + 1 + rand();
  18     return [[start, rand()]].concat(make_random_table(end));
  19   }
  20   return tax_table_from_table(make_random_table());
  21 }
  22
  23 test("parse tax table", () => {
  24   const parsed = parse_tax_table(' 1  2\n10  4\n');
  25   assert.strictEqual(parsed.length, 2);
  26   assert.deepStrictEqual(parsed[0], [1, 10, .02]);
  27   assert.deepStrictEqual(parsed[1], [10, Infinity, .04]);
  28 });
  29
  30 test("sum", () => {
  31   assert.strictEqual(sum([]), 0);
  32   assert.strictEqual(sum([7]), 7);
  33   assert.strictEqual(sum([100, 1, 10]), 111);
  34 });
  35
  36 test("tax", () => {
  37   assert.strictEqual(tax([[10, 100, .01], [100, Infinity, .1]], 150), 5.9);
  38 });
  39
  40 test("merge tax tables", () => {
  41   for (var i = 0; i < 1000; i++) {
  42     const t1 = make_random_tax_table();
  43     const t2 = make_random_tax_table();
  44     const combined = merge_tax_tables(t1, t2);
  45     for (var j = 0; j < 10; j++) {
  46       const income = rand(250);
  47       assert.ok(near(tax(t1, income) + tax(t2, income), tax(combined, income)));
  48     }
  49   }
  50 });
  51
  52 test("invert", () => {
  53   assert.strictEqual(invert([                  ])(10), 10);
  54   assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
  55   assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
  56   assert.strictEqual(invert([[10, Infinity, .1]])( 9),  9);
  57   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);
  58   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(112), 127.5);
  59   assert.strictEqual(invert([[6, 90, 0.75], [90, Infinity, 0.12]])(27), 90);
  60
  61   for (var i = 0; i < 1000; i++) {
  62     const t = make_random_tax_table();
  63     const inverted_t = invert(t);
  64     for (var j = 0; j < 20; j++) {
  65       const net = rand(250);
  66       const gross = inverted_t(net);
  67       assert.ok(near(net, gross - tax(t, gross)));
  68     }
  69   }
  70 });