The hydro test pressure is calculated by the software used for the design of the vessel. You, as a fabricator not responsible for the design of the vessel, you were suppose to be given the test pressure by your Client. Did you agree to become part of the design liability, by accepting to provide the hydro testing design to your Client? Who's calculated or nominated the MAWP, which enables the calculation of the hydro test pressure? Refer to UG-99(b) below:
(b) Except as otherwise permitted in (a) above and
27-4, vessels designed for internal pressure shall be subjected to a hydrostatic test pressure which at every point in the vessel is at least equal to 1.3 times the maximum allowable working pressure to be marked on the vessel multiplied by the lowest ratio (for the materials of which the vessel is constructed) of the stress value S for the test temperature on the vessel to the stress value S for the design temperature (see UG-21). All loadings that may exist during this test shall be given consideration.
Please note the test pressure at any point shall be at least 1.3 x MAWP, for any horizontal or vertical testing method. That means it can be higher than 1.3 x MAWP, but not to the extent of overstressing the material, any near the yield limit.
Safer still, ask your Client to provide the test pressure calculations which you feel confortable with.