UI

[inverse-tax] / tax.test.js

diff --git a/tax.test.js b/tax.test.js
index b4959184215ac9b7a7c27c1a4a18f1216b5c5a3f..21b98b62a01955df27e6c9e2931c40ae66e385d9 100644 (file)
--- a/tax.test.js
+++ b/tax.test.js
@@ -10,7 +10,7 @@ function near(a, b, epsilon = 1e-6) {
   return Math.abs(a - b) < epsilon;
 }
 
-function rand(limit = 100) {
+function rand(limit = 99) {
   return Math.round(Math.random() * limit);
 }
 
@@ -57,5 +57,18 @@ test("invert", () => {
   assert.strictEqual(invert([                  ])(10), 10);
   assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
   assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
+  assert.strictEqual(invert([[10, Infinity, .1]])( 9),  9);
   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);
+  assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(112), 127.5);
+  assert.strictEqual(invert([[6, 90, 0.75], [90, Infinity, 0.12]])(27), 90);
+
+  for (var i = 0; i < 1000; i++) {
+    const t = make_random_tax_table();
+    const inverted_t = invert(t);
+    for (var j = 0; j < 20; j++) {
+      const net = rand(250);
+      const gross = inverted_t(net);
+      assert.ok(near(net, gross - tax(t, gross)));
+    }
+  }
 });