Updated the test system

test/rearg.test.js

@@ -0,0 +1,15 @@
+const expect = require('expect');
+const {rearg} = require('./_30s.js');
+
+test('rearg is a Function', () => {
+  expect(rearg).toBeInstanceOf(Function);
+});
+var rearged = rearg(
+  function(a, b, c) {
+    return [a, b, c];
+  },
+  [2, 0, 1]
+);
+test('Reorders arguments in invoked function', () => {
+  expect(rearged('b', 'c', 'a')).toEqual(['a', 'b', 'c']);
+});