The most important part about long range testing is to have a good area with multiple "safe zones" along the return flight path for emergency landings if battery power gets too low and your bird won't make it back to you.
I fly at a public park near Cincinnati, OH, and it's flat as a pancake and very few trees in any direction. The park itself is one square mile but I like to fly beyond the borders so it's an ideal location for long distance testing. However, back in October on a windless day I tried pushing the limits too much on my P4 and flew out 4.5 miles on a stock battery and it got down to 7% power when it was still a mile away from me coming home! Luckily, there is an area north of the park that is an undeveloped housing project with multiple paved roads but no houses. So I was able to land in that "safety zone" since I still had FPV signal even at 2% battery power and was able to gently bring it down in a patch of thick grass. Careful planning was what saved me from losing a $1200 bird.
