Migrated tests to jest

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

test3/isPlainObject/isPlainObject.js

@@ -0,0 +1,2 @@
+const isPlainObject = val => !!val && typeof val === 'object' && val.constructor === Object;
+module.exports = isPlainObject;

test3/isPlainObject/isPlainObject.test.js

@@ -0,0 +1,10 @@
+const expect = require('expect');
+const isPlainObject = require('./isPlainObject.js');
+
+test('Testing isPlainObject', () => {
+  //For more information on all the methods supported by tape
+  //Please go to https://github.com/substack/tape
+  expect(typeof isPlainObject === 'function').toBeTruthy();
+  expect(isPlainObject({ a: 1 })).toBe(true);
+  expect(isPlainObject(new Map())).toBe(false);
+});