Since testing illuminates the risks in a project, the sooner everyone sees those risks, the better. In a serial life cycle, bring the testers in during requirements. Ask for their feedback about product requirements. In an iterative life cycle, ask the testers to help evaluate prototypes. In an incremental life cycle, have the testers start testing features as soon as there are any to test. And in an agile life cycle, make sure the testers work with both the developers to develop the technology-facing tests and with the product owners to develop customer-facing tests.