Depends on:
Test pressure and what that is in terms of % SMYS of your pipe
What the min and max elevation is along your pipe. YOui would be surprised what "almost flat" means to different people.
Calculate the difference in head between test pressure at the highest point (usually the test requirement) and pressure at the lowest point.
Then see if the pressure at the lowest point results in an SMYS of 90% or less.
If it is then you're ok, if not then you need to segment up the pipeline.
You commonly find the min to max elevations is in the order of 125 to 150m, but each pipeline is different.
Post the full elevation vs distance, pipe size, wall thickness , SMYS and test pressure and then we can have a better look.
This is pretty basic stuff though - Is there no one in your company who can help you?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.