We've put together a lot of building blocks for our test website. We have a database of tests, and we've built functions to run different type of tests. We can access our site and check if we are seeing the right page. We can check that all the files are where we expect them to be, on the remote server. We can automatically run functions on the site and get it to optimize itself. It's fairly simple to write code that uses these tools to run a suite of tests whenever we want—when we log on or by some automatic reminder, such as setting a Cron job on a Linux server to run our program at suitable intervals.
It's not really enough to run tests and just store the results in a database. If something is wrong, we need to know it as soon as possible. Here CI's email class comes in. It allows us to program our site to send emails whenever certain conditions are met. You might want to send an email for each failed test, or you might want to run a series...