invert

[inverse-tax] / tax.test.js

diff --git a/tax.test.js b/tax.test.js
index 6fcc15c74dbc39ad806c7c3961b495360ed7edf1..479323bf3b671436756c5e7d022b305b61ff08b6 100644 (file)
--- a/tax.test.js
+++ b/tax.test.js
@@ -22,3 +22,30 @@ test("sum", () => {
 test("tax", () => {
   assert.strictEqual(tax([[10, 100, .01], [100, Infinity, .1]], 150), 5.9);
 });
+
+test("merge tax tables", () => {
+  function rand(limit = 100) {
+    return Math.round(Math.random() * limit);
+  }
+  function make_random_tax_table(min_threshold) {
+    if (rand(2)) return [];
+    const start = min_threshold === undefined ? rand() : min_threshold;
+    const end = start + 1 + rand();
+    return [[start, end, rand()]].concat(make_random_tax_table(end));
+  }
+  for (var i = 0; i < 1000; i++) {
+    const t1 = make_random_tax_table();
+    const t2 = make_random_tax_table();
+    const combined = merge_tax_tables(t1, t2);
+    for (var j = 0; j < 10; j++) {
+      const income = rand(250);
+      assert.strictEqual(tax(t1, income) + tax(t2, income), tax(combined, income));
+    }
+  }
+});
+
+test("invert", () => {
+  assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
+  assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
+  assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);
+});