Software testing plays an important role in the process of verifying software functionality and preventing bugs in production code. By writing automated tests using code instead of conducting manual tests, the amount of tedious work during the development process can be reduced and the software quality can be improved. This thesis presents the results of a conducted case study on how automated testing can be used when implementing new functionality in a Ruby on Rails web application. Different frameworks for automated software testing are used as well as test-driven development methodology, with the purpose of getting a broad perspective on the subject. This thesis studies common issues with testing web applications, and discuss drawbacks and advantages of different testing approaches. It also looks into quality factors that are applicable for tests, and analyze how these can be measured.