In general, yes. However, you need to be careful in the case of large vapor lines. These will not normally have a liquid load in operation and a hydrotest may impose loads on the structure and equipment that could be impractical for the civil/structural engineers to support. The project may opt to pneumatically test in these cases.

At my company, we design for full water loads on all lines up to 24" diamter. Above that, liquid lines are still designed always for full load. Vapor service lines are discussed with the project team to assess the impact.

And, there's always a but - if you have springs in your system, you need to make sure the operating case you design them to uses the actual SG of the fluid. It doesn't affect smaller lines too much, but 6"+ you really don't want to size a spring that is supporting a vapor lines based on the liquid full condition. It will end up pulling up way too hard.