Which scenario would most likely require testing of drainage and venting systems?

The scenario that would most likely require testing of drainage and venting systems is the installation of new fixtures. When new fixtures are added to a plumbing system, it's essential to ensure that the drainage and venting systems can handle the additional flow and pressures introduced by the new installations. Testing confirms that waste can be effectively transported away from the fixtures and that the venting pipes are properly configured to prevent issues such as siphoning or back pressure, which could lead to improper drainage or unpleasant odors.

The interaction of new fixtures with existing plumbing networks necessitates thorough testing to ensure compliance with building codes and to maintain system integrity. This process helps to alleviate potential future problems that could arise from inadequate drainage or improper venting, thereby ensuring reliable operation of the plumbing system as a whole.