get stripe tests working again

Some problems we have:

• Our testing.md doc says the tests aren't updated and contains old information
• I think the katalan tests are too hard to maintain and should be abandoned. Perhaps another issue could be opened to revisit whether we want to rebuild them
• We need to update our base test to better match the phpUnit test base framework
• I'm getting an error when i try to run a test: PHP Fatal error: Trait 'CRM_Core_Payment_MJWTrait' not found in /var/www/civicrm/civicrm-buildkit/build/mycivi/web/sites/default/files/civicrm/ext/stripe/CRM/Core/Payment/Stripe.php on line 13