Updated the test system

test/unionWith.test.js

@@ -0,0 +1,11 @@
+const expect = require('expect');
+const {unionWith} = require('./_30s.js');
+
+test('unionWith is a Function', () => {
+  expect(unionWith).toBeInstanceOf(Function);
+});
+test('Produces the appropriate results', () => {
+  expect(
+    unionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b))
+  ).toEqual([1, 1.2, 1.5, 3, 0, 3.9]);
+});