Migrated tests to jest

Used jest-codemods to migrate, will have to pass everything by hand before we can merge.

test4/join/join.js

@@ -0,0 +1,11 @@
+const join = (arr, separator = ',', end = separator) =>
+arr.reduce(
+(acc, val, i) =>
+i === arr.length - 2
+? acc + val + end
+: i === arr.length - 1
+? acc + val
+: acc + val + separator,
+''
+);
+module.exports = join;

test4/join/join.test.js

@@ -0,0 +1,11 @@
+const expect = require('expect');
+const join = require('./join.js');
+
+test('Testing join', () => {
+  //For more information on all the methods supported by tape
+  //Please go to https://github.com/substack/tape
+  expect(typeof join === 'function').toBeTruthy();
+  expect(join(['pen', 'pineapple', 'apple', 'pen'], ',', '&')).toEqual("pen,pineapple,apple&pen");
+  expect(join(['pen', 'pineapple', 'apple', 'pen'], ',')).toEqual("pen,pineapple,apple,pen");
+  expect(join(['pen', 'pineapple', 'apple', 'pen'])).toEqual("pen,pineapple,apple,pen");
+});