Here is the fifth video in our series designed to jump-start your understanding of the core practices and principles of Agile Software Engineering (ASE). In this installment, Lean-Agile thought leader Ken Pugh talks about the significant advantages of an ‘always-think-testing’ approach. By thinking about testing early in the development process (‘shifting testing left’), we can avoid the exponentially higher costs of finding defects late in the timeline from requirements definition to production. Shifting testing left.