Test migration to jest by hand

Apparently using regular expressions is way easier.

test/head/head.js

@@ -0,0 +1,2 @@
+const head = arr => arr[0];
+module.exports = head;

test/head/head.test.js

@@ -0,0 +1,24 @@
+const expect = require('expect');
+const head = require('./head.js');
+
+
+  test('head is a Function', () => {
+  expect(head).toBeInstanceOf(Function);
+});
+  test('head({ a: 1234}) returns undefined', () => {
+  expect(head({ a: 1234}) === undefined).toBeTruthy();
+});
+  t.equal(head([1, 2, 3]), 1, "head([1, 2, 3]) returns 1");
+  t.equal(head({ 0: false}), false, 'head({ 0: false}) returns false');
+  t.equal(head('String'), 'S', 'head(String) returns S');
+  t.throws(() => head(null), 'head(null) throws an Error');
+  t.throws(() => head(undefined), 'head(undefined) throws an Error');
+  t.throws(() => head(), 'head() throws an Error');
+
+  let start = new Date().getTime();
+  head([1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 1122, 32124, 23232]);
+  let end = new Date().getTime();
+  test('head([1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 1122, 32124, 23232]) takes less than 2s to run', () => {
+  expect((end - start) < 2000).toBeTruthy();
+});
+