Updated the test system

test/unionBy.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {unionBy} = require('./_30s.js');
+
+test('unionBy is a Function', () => {
+  expect(unionBy).toBeInstanceOf(Function);
+});
+test('Produces the appropriate results', () => {
+  expect(unionBy([2.1], [1.2, 2.3], Math.floor)).toEqual([2.1, 1.2]);
+});