No statute - the days of prescripitive requiremets for frequency & type are over. There is instead a variety of differing guidance and you base your actions on that andthe risks present at your site.
If you are in a normal risk premises and are looking at discounting an exit due to the 'fire' then it should reflect likely occurances. Unless there is a catastrophic failure in precautions or a 1 in a million event like a plane crashing into you then regardless of building size (within reason) there should only be one exit from the fire floor or in a worst case situation one stairway blocked in most cases, unless you want to simulate multiple seat arson or a major explosion you shouldn't need to thus 'block' one floors exit or one stairwell.
In a perfect world everyone is always keeping an eye on precautions all the time, but normally recorded formal in house checks are weekly or daily (although again it's all risk specific).
Fire wardens training if good, usually goes a bit further than just action upon alarm to include FP, and they are usually useful for checking their areas, leaving facilities/building management to concentrate on circulation route & plant, plus site wide systems.
One premises we deal with has a system that after the weekly fire alarm test wardens send a checkbox ticket to the FM that not only confirms the sounders in their area worked, but they have carried out a check on extinguishers, MoE, doors, etc
