Robert Auger (www.qasec.com) has written an excellent article about how the Quality Assurance phase of the development cycle can incorporate security testing into a standard test plan, and make it part of the regular testing cycle.

From the article :

"Part of software testing involves replicating customer use cases against a given application. These use cases are documented in a test plan during the quality assurance phase in the development cycle to act as a checklist ensuring common use cases aren’t missed during the testing phase. People within the quality assurance community are starting to understand that checking an application for security issues (defects) isn’t just the responsibility of the security department (if one exists), or the software architects"

Check the whole article here : http://www.qasec.com/cycle/securitytestcases.shtml