Updated the test system

test/unary.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {unary} = require('./_30s.js');
+
+test('unary is a Function', () => {
+  expect(unary).toBeInstanceOf(Function);
+});
+test('Discards arguments after the first one', () => {
+  expect(['6', '8', '10'].map(unary(parseInt))).toEqual([6, 8, 10]);
+});