Incorporate iATS tests into core tests as much as possible

Examine iATS test suite maintained by KarinG at https://github.com/iATSPayments/com.iatspayments.civicrm#testing and create a test in core for each one as much as possible.

Tim Otten and Coleman Watts in the absence of Eileen McNaughton can you
1) Confirm that testing of iATS extension for payment processing in core is Okay (cf CRM-19799), and that test suite should call to install and enable this extension?
2) Recommend an approach to screen scraping (perhaps just regular Selenium) to automate steps 6 and 7?
3) Suggest an approach to creating a special test job that will complete a test after a long delay in order to handle steps 9 and 10.

Should we make a parallel set of tests for a non-iATS payment processor like PayPal Pro?

Document here in issue description which tests have been and have not been implemented.