In my Evaluating the User Interface and User Experience presentation at the Boston Design 4 Drupal camp, I touched on the need for designers to check the color contrast between foreground and background page elements, to ensure the color combination is usable and accessible to all.

Selenium IDE is a free Firefox add-on that is used for automated website testing. One can record their mouse and keyboard inputs and create a 'test case'. Further customizion (i.e. confirming a phrase appears) can be done using Selenium or a text editor. One can then play back their test in Firefox and Selenium IDE will flag any errors or mismatches to the test case. Mostly I've used it to test Plone sites and bulletin boards. It's a brilliant tool for any development team.