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 a very dangerous
shock if the metal were to come live 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 your 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 also an overall Visual Inspection.