Tracer Bullet Testing or Synthetic Transactions or Synthetic Monitoring is a way of testing your service/app in production where its supposed to run but without affecting users/clients/external systems.

Monitoring the health of your application in production is a crucial aspect of software development because at any given point in time, you want to be reasonably certain about how your business critical application is performing and you want to be alerted to any problems that might be brewing up in the application before your customers do.