Well, if you just installed the lines, then you shut off all the valves & pressure test the new lines - if you want to bother.
The propane company had their guy install the lines originally for our propane. When I put in the new line, I replaced all of the shoddy work that he did. In fact, it was his work that was one of the reasons that led to the remodeling job. He put the nut over the copper line, flared the copper, THEN drilled a hole through the house big enough for that nut to easily go through. And, he didn't make any attempt to seal off that hole. That led to a rodent penetrating the wall from the outside & using the insulation inside our oven as its home. Our old stove was consequently ruined. But, since I had a much longer run to make for the oven's new location, and I used gas tite instead of copper, I wasn't going to screw around with various fittings to make it work - I just replaced the line to the dryer. And later, I added in another line to the new propane hot water tank. (I now have two hot water tanks - one propane & one oil, with valves so I can control which is being used.)