Updated the test system

test/findLastKey.test.js

@@ -0,0 +1,18 @@
+const expect = require('expect');
+const {findLastKey} = require('./_30s.js');
+
+test('findLastKey is a Function', () => {
+  expect(findLastKey).toBeInstanceOf(Function);
+});
+test('eturns the appropriate key', () => {
+  expect(
+    findLastKey(
+      {
+        barney: { age: 36, active: true },
+        fred: { age: 40, active: false },
+        pebbles: { age: 1, active: true }
+      },
+      o => o['active']
+    )
+  ).toBe('pebbles');
+});