Code level: Unit tests, peer-reviews. Integration: Automated UI testing. Functional: Humans, lots of them. Startups usually have very small teams. Take advan

Code level: Unit tests, peer-reviews. Integration: Automated UI testing. Functional: Humans, lots of them. Startups usually have very small teams. Take advantage of tools that do stuff for you. Also, having other members of the team take part in testing is a means to get to know the team better and learn something new.