This document discusses several software development life cycle models and their implications for testing. It describes the V-model, which uses four levels of testing: component, integration, system, and acceptance testing. Iterative life cycles involve multiple smaller development cycles with incremental additions of functionality and regression testing across iterations. Rapid application development encourages active customer feedback and early validation. Agile methods like Extreme Programming integrate testing activities into frequent development cycles with automated unit testing and integration testing occurring daily. Regardless of the model, testing activities should correspond to development and begin during planning to effectively test each level.