If you put the nRF51822 in a weak magnetic field nothing will happen. If you put nRF51 in a strong magnetic field it will reset. If you put nRF51 in an extreme metal field it will break.
There are tests that can be done, what are your concerns?
will need magnetic body at both top side and bottom side of PCBA,
want to konw if necessary to add protection or other way to avoid the effect.
any kind of this case do you met before?
Unfortunately I have not met this kind of case before, I'd advise to set up a testbench as see how it performs. Take the magnets you intend to use, and glue/tape them to the development kit and see what happens, if the device is able to keep turned on, i.e. not constantly resetting, you should investigate the signal characteristics with a spectrum analyzer. High H-fields from the magnets could cause disturbance in the RF-modulation and transmission characteristics.
