A key to working out details of integrations is to iterate with various parties involved. Get things live faster by dramatically improving that loop.
Test with a framework designed for integrations
Prismatic's testing framework provides a sandbox that's easy to use and nearly identical to production. This provides a simple yet robust way to deploy integrations for testing, while capturing all the data you need during the process.
Make changes quickly
The faster you can make changes during the testing process, the sooner you can get to production. Whether the change needed is configuration - such as config variables or credentials - or logic in the integration itself, you have the tools at your fingertips to make it quickly and continue testing.
This iteration cycle dramatically decreases the amount of back and forth between everyone involved, getting you where you need to be quickly and with miminal hassle.
Information for everyone who needs it
A huge part of testing is being able to quickly see what's going on. The testing framework includes a test run viewer to show every run that's taken place with all the log data in real time.
This is indispensable for your team, and can also be provided to customers and third parties during the testing process using the customer portal. This allows everyone to see what's going on and makes the process much faster.