Test migration to jest by hand

Apparently using regular expressions is way easier.

test/mapKeys/mapKeys.test.js

@@ -0,0 +1,10 @@
+const expect = require('expect');
+const mapKeys = require('./mapKeys.js');
+
+
+  test('mapKeys is a Function', () => {
+  expect(mapKeys).toBeInstanceOf(Function);
+});
+  t.deepEqual(mapKeys({ a: 1, b: 2 }, (val, key) => key + val), { a1: 1, b2: 2 }, 'Maps keys');
+  
+