Updated the test system

test/sortedLastIndex.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {sortedLastIndex} = require('./_30s.js');
+
+test('sortedLastIndex is a Function', () => {
+  expect(sortedLastIndex).toBeInstanceOf(Function);
+});
+test('Returns the highest index to insert the element without messing up the list order', () => {
+  expect(sortedLastIndex([10, 20, 30, 30, 40], 30)).toBe(4);
+});