Updated the test system

test/stableSort.test.js

@@ -0,0 +1,11 @@
+const expect = require('expect');
+const {stableSort} = require('./_30s.js');
+
+test('stableSort is a Function', () => {
+  expect(stableSort).toBeInstanceOf(Function);
+});
+const arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+const compare = () => 0;
+test('Array is properly sorted', () => {
+  expect(stableSort(arr, compare)).toEqual(arr);
+});