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 near(a, b, epsilon = 1e-6) {
  10   return Math.abs(a - b) < epsilon;
  11 }
  12
  13 function rand(limit = 99) {
  14   return Math.round(Math.random() * limit);
  15 }
  16
  17 function make_random_tax_table() {
  18   function make_random_table(min_threshold) {
  19     if (rand(2)) return [];
  20     const start = min_threshold === undefined ? rand() : min_threshold;
  21     const end = start + 1 + rand();
  22     return [[start, rand()]].concat(make_random_table(end));
  23   }
  24   return tax_table_from_table(make_random_table());
  25 }
  26
  27 test("parse tax table", () => {
  28   const parsed = parse_tax_table(' 1  2\n10  4\n');
  29   assert.strictEqual(parsed.length, 2);
  30   assert.deepStrictEqual(parsed[0], [1, 10, .02]);
  31   assert.deepStrictEqual(parsed[1], [10, Infinity, .04]);
  32 });
  33
  34 test("sum", () => {
  35   assert.strictEqual(sum([]), 0);
  36   assert.strictEqual(sum([7]), 7);
  37   assert.strictEqual(sum([100, 1, 10]), 111);
  38 });
  39
  40 test("tax", () => {
  41   assert.strictEqual(tax([[10, 100, .01], [100, Infinity, .1]], 150), 5.9);
  42 });
  43
  44 test("merge tax tables", () => {
  45   for (var i = 0; i < 1000; i++) {
  46     const t1 = make_random_tax_table();
  47     const t2 = make_random_tax_table();
  48     const combined = merge_tax_tables(t1, t2);
  49     for (var j = 0; j < 10; j++) {
  50       const income = rand(250);
  51       assert.ok(near(tax(t1, income) + tax(t2, income), tax(combined, income)));
  52     }
  53   }
  54 });
  55
  56 test("invert", () => {
  57   assert.strictEqual(invert([                  ])(10), 10);
  58   assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
  59   assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
  60   assert.strictEqual(invert([[10, Infinity, .1]])( 9),  9);
  61   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);
  62   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(112), 127.5);
  63   assert.strictEqual(invert([[6, 90, 0.75], [90, Infinity, 0.12]])(27), 90);
  64
  65   for (var i = 0; i < 1000; i++) {
  66     const t = make_random_tax_table();
  67     const inverted_t = invert(t);
  68     for (var j = 0; j < 20; j++) {
  69       const net = rand(250);
  70       const gross = inverted_t(net);
  71       assert.ok(near(net, gross - tax(t, gross)));
  72     }
  73   }
  74 });