Payment tests refactor (#9695)

* Reorganized files, reduced function size, reduced duplication

* Refactored amazon tests organization

* Reduced duplication

* Reorganized paypal tests

* Reorganized stripe tests

* Fixed lint issues

* Fixed gem purchase expectations

* Added cloning so we don't modify the common block

test/api/v3/unit/libs/payments/paymentHelpers.js

@@ -0,0 +1,7 @@
+import { model as User } from '../../../../../../website/server/models/user';
+
+export async function createNonLeaderGroupMember (group) {
+  let nonLeader = new User();
+  nonLeader.guilds.push(group._id);
+  return await nonLeader.save();
+}