plone.act is deprecated.
Please, use http://pypi.python.org/pypi/plone.app.robotframework instead.
plone.act and its documentation gives you everything to get started in writing and executing functional Selenium tests (including acceptance tests) for your Plone add-on.
Robot Framework is a generic test automation framework for acceptance testing and acceptance test-driven development (ATDD), even for behavior driven development (BDD). It has easy-to-use plain text test syntax and utilizes the keyword-driven testing approach. Selenium is a web browser automation framework that exercises the browser as if the user was interacting with the browser.