Final answer:
The welder test where a pipe assembly is placed vertically and welded horizontally without rotating the assembly is referred to as the 5G welding position.
Step-by-step explanation:
The welder test described in the question is known as the 5G position. In the 5G welding position, a pipe assembly is placed vertically, and the joint is welded horizontally. The welder works around the pipe, which remains stationary and is not rotated during the process. This is a common test for certifying pipe welders, as it simulates conditions that may be encountered in fieldwork, such as in pipeline welding, where the pipes cannot be easily rotated due to their fixed installation.