SET means Software engineer in Testing. The job which is responsible for the complete design of the test cases and to maintain them.
As a Software Engineer in Test, you have the opportunity to accelerate the delivery and to improve the quality of Google products. You will be responsible for designing and implementing development and test infrastructure. You will be part of an Engineering team that is working on problems in a number of areas, including caching optimizations, content delivery, network protocols, machine learning, and mobile products. Your focus is developing code rather than fixing or finding bugs. Your job is to accelerate product development by helping developers help themselves.