Updated the test system

test/attempt.test.js

@@ -0,0 +1,16 @@
+const expect = require('expect');
+const {attempt} = require('./_30s.js');
+
+test('attempt is a Function', () => {
+  expect(attempt).toBeInstanceOf(Function);
+});
+test('Returns a value', () => {
+  expect(attempt(() => 0)).toBe(0);
+});
+test('Returns an error', () => {
+  expect(
+    attempt(() => {
+      throw new Error();
+    })
+  ).toBeInstanceOf(Error);
+});