The wiring of the building will be checked using thermal imaging to spot any hidden electrical issues.
Fixed metal assets will be checked to ensure earthing is in place to avoid an extremely dangerous shock if the metal where to come alive for any reason.
The fuse board will be inspected to ensure it is in good health and a trip test will be conducted on RCBs to ensure if there is a surge you fuse board would block it and keep you safe.
They are the key checks but there are also many more conducted such as Polarity Testing, Earth Electrode Inspection and an overall Visual Inspection.
An electrical installation should be inspected and tested at regular intervals to ensure they are in a satisfactory condition for continues use