Test migration to jest by hand

Apparently using regular expressions is way easier.

test/sumBy/sumBy.js

@@ -0,0 +1,3 @@
+const sumBy = (arr, fn) =>
+arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0);
+module.exports = sumBy;

test/sumBy/sumBy.test.js

@@ -0,0 +1,8 @@
+const expect = require('expect');
+const sumBy = require('./sumBy.js');
+
+
+  test('sumBy is a Function', () => {
+  expect(sumBy).toBeInstanceOf(Function);
+});
+