You should rely on the piping code that the pipe has been designed to.

The hydrostatic test pressure relies on the design pressure/temperature and test temperature, which relies on the thickness of the pipe, which is dependent on the strength and material specification of the pipe.

Have a search through this site with the menu at the right (first try "hydrostatic test")

test at 125% of the operating pressure

Listen to xMech - ignore Moore. Everyone will live longer.

As suggested, you need to look at the piping code you are using.

Some piping codes will require the hydrotest be done at 150% of design pressure (B31.3 for example), others have lower pressure requirements but may require you to hold those pressures for a specific period of time.