Question:

How AutoPIPE Vessel calculates the Hydrotest MAWP for both the shell side and the tube side ?

Answer: 

The Maximum Allowable Working Pressure (MAWP) is calculated for each component of the equipment. The lowest MAWP value among these components is considered as the MAWP for the entire equipment and is used in hydrotest pressure calculations.

You can find the formula under the component design calculations section: