Paypal Integration Testing...

1. Get details of dummy credit card
2. Checkout button --> Paypal --> Paypal gateway processing --> Back to your website
3. Check for session expiry, session ends.
4. Check what happens if Payment Gateway stops responding.
5. Check for data going to the backend.
6. What happens upon successful transaction -- database, messages, etc.
7. Check receipts are generated and sent to customer email account

Shift Left (Courtesy BMC)

Shift left is a software testing approach where software testing is performed (moved or shifted) to the left / earlier in the Life-cycle. This basically is "Test Early and Test Often".

• In the Traditional Model, requirements and design happen to the left, and testing of those requirements to the right. As the project progresses, the testing effort increases. 
• Consequently later the defects are found, the costlier it becomes to fix those bugs

• In Shift Left, testing is performed during early stages by engaging early in the project lifecycle. 

7 Principles of Software Testing...