Updated the test system

test/dropWhile.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {dropWhile} = require('./_30s.js');
+
+test('dropWhile is a Function', () => {
+  expect(dropWhile).toBeInstanceOf(Function);
+});
+test('Removes elements in an array until the passed function returns true.', () => {
+  expect(dropWhile([1, 2, 3, 4], n => n >= 3)).toEqual([3, 4]);
+});