Certification requirements are CS 25 121 (D) in EASA land. Solely considers 1 engine inoperative, multiple failures not required. 25.119 covers all engines operating. The manufacturer is required t9 give you performance data to calculate your actual performance in the multiple failure scenario.
If you an Airbus driver relying on Flysmart you will note that even with LG RETRACT on the INOP SYS FS does not assume gear stuck down when calculating approach climb gradient and it has to be manually selected.