• howto:webapp_monitoring_2_0

• http://www.agileatwork.com/the-holy-trinity-of-web-2-0-application-monitoring/
• http://www.sage.org/lists/sage-members-archive/2008/msg00027.html
• http://www.alittlemadness.com/2008/03/05/running-selenium-headless/

If I had to pick one type of testing it would be to test the end-user functionality of the system. The important thing to consider is the user. While testing things like database availability, server up-time, etc, are all important, testing work-flows through your system via a remote UI testing system covers all these bases. If you know that the critical parts of your system are available to the end-user, then you know your system is prolly Ok.

1. Identify the important work-flows in your system. For example, if you wrote an eCommerce site you might identify a work-flow of “search for a product, put product in shopping cart, and purchase product”.
2. Prioritize the work-flows, and build out higher-priority tests first. You can always add additional tests after you roll out to production.
3. Build UI tests using one of the available UI testing frameworks. There are a number of free and commercial UI testing frameworks that can be run in an automated fashion. Build a core set of tests first that address critical work-flows.
4. Setup at least one remote location from which to run tests. You want to test every aspect of your system, which means testing it remotely. Is the internet connection up? Is the web server running? Is the connection to the database server working? Etc, etc. If you test remotely you make sure you system is available to the outside world which means it is most likely working end-to-end. You can also run these tests internally, but I think it is critical to run them externally.
5. Make sure your solution includes both reporting and notification. If one of your critical work-flow tests fails, you want someone to know about it to fix the problem ASAP. If a non-critical task fails, perhaps you only want reporting so that you can fix problems out-of-band.

This end-user testing should not eliminate monitoring of system in your data-center, but I want to reiterate that end-user testing is the most important type of testing you can do for a web application.