To prevent business failure on your website, you must test: stress test, load test, and performance test. This must be done from beginning to end. The approach of "test early, test often" is unfortunately not adhered to by most companies, and test efforts are usually left to the last minute. Companies hence struggle to test critical functionalities and transactions before the software's release date.

It is important to understand the impact of failure on the business, and working backwards, mitigate those risks by ranking each test as early as possible so as to align these tests with the business requirement that drives them. When transactions are critical to business success, they must be thoroughly tested from both a functional and nonfunctional perspective. This is to see if the application correctly performs the transaction in a timely fashion for all users, regardless of how they access the application. Even after the software goes live, continuous and regular testing of its critical transactions is important.

Automated tests should be developed as early as possible and re-run regularly to ensure development efforts don't break the application. These automated tests should cover the developer's code, functionality of key transactions and application performance.

http://www.zdnet.com/software-testing-lacking-serious-effort-7000002324/