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Tests is well established and all applications ideally complete a suite of unit tests. However, in the real world, not all applications possess these ideal qualities. In reality, developers have to work with applications that are not well designed/developed and that may not have had any unit testing. This makes modifying/enhancing these applications riskier.
In such circumstances, running automated integration tests might be quicker and just as effective. The integration tests will allow you to modify/enhance theapplication with confidence. Integration tests also test the application as a whole, which unit tests do not. Unit tests execute only a part of the application in isolation. While integration tests can detect issues in any of the application's components, unit tests detect issues only within a particular component.
Automated integration tests can be useful particularly for legacy applications, CRUD applications and applications that have business logic tightly coupled to the environment in which they run. The Selenium web application testing system is a powerful tool for implementing automated integration testing for Java-based web applications. In his Web Developer's Virtual Library (WDVL) article, "Selenium: Automated Integration Testing for Java Web Apps," Avneet Mangat explains automated integration testing with Selenium. You will learn how to develop integration tests using the Selenium IDE, how to export the integration tests as JUnit tests, and then how to automate test execution.

Read the full story at Web Developer's Virtual Library:
Selenium: Automated Integration Testing for Java Web Apps