I would like to make integration tests and system tests for my applications but producing good integration and system tests have often needed so much effort that I have not bothered. The few times I tried, I wrote custom, application-specific test harnesses, which felt like re-inventing the wheel each time. I wonder if this is the wrong approach. Is there a "standard" approach to integration and full system testing?

EDIT: To clarify, it's automated tests, for desktop and web applications. Ideally a complete test suite that exercises the full functionality of the application.