Updated the test system

test/flip.test.js

@@ -0,0 +1,13 @@
+const expect = require('expect');
+const {flip} = require('./_30s.js');
+
+test('flip is a Function', () => {
+  expect(flip).toBeInstanceOf(Function);
+});
+let a = { name: 'John Smith' };
+let b = {};
+const mergeFrom = flip(Object.assign);
+let mergePerson = mergeFrom.bind(null, a);
+test('Flips argument order', () => {
+  expect(mergePerson(b)).toEqual(a);
+});