The gate at the end of the stage is to ensure the correct artefacts have been produced to assure the application or system has been created according to requirements and specification, and that it works according to expectations, without adversely impacting the live environment.
The Project Manager coordinates the development of the system or application and its testing to ensure fitness for purpose (utility) and fitness for use (warranty).
If the Build and Test Stage is approved, the Project Board authorises progress to the Transition Stage.