Any building has to have some one appointed as building manager, and he decides how much and how often the building is inspected and tested, so as an electrician we get told what the procedure is, often your required to check so many items and if all OK then that's it, and the items are listed, so next tester does not select same items, we are given the last report and we look for any degrade in test results, and should we find faults then we test more. Also common to test yearly so over 5 years every item has been tested, this seems to satisfy the HSE.
However on domestic often we are not give previous results, and may have been 10 years since last test, but in England and Wales it is still down to the owner to say how much is to be tested, Scotland testing is required by law for rented accommodation so I would guess the law says what must be tested, but else where it is normally the scheme provider who advises members what they should test and how deep they should go, however there was a directive that just because there is no loft lid, that does not mean cables in the loft don't need inspecting not sure how though, suppose one has to lift roof tiles?
In the main testers have taken the C&G2391 exam and the course so follow what they were taught, in my case that was 15 years ago so tend to use the electrical safety council best practice guide. But other than Scotland there is no law about how often or what must be inspected or tested, industrial premises the HSE will expect it to be all tested every 5 years, but often it is done at 20% each year unless faults found.
The result is the cost can vary a lot, it is unlikely that you can test a house in less than 1/2 a day, it could easy take all day, but for rented accommodation where it is inspected and tested every time the occupant changes, it could be very apparent nothing has changed since last one, so the tester may only test 10% just to verify. The house may have already been tested 5 time that year, so all the guy is looking for is changes made by the tenant.
Where a property fails, then it is reasonable again for the tester not to continue, as clear work done after will invalidate his test, however some testers use this as a get out, they hunt for faults, as once found they can stop testing that circuit, so you get a report which shows one fault per circuit some times these faults seem fictional with the tester being rather vague as to exactly what has been found. I have seen reports where it simply says asbestos found testing abandoned, this asbestos was a little tiny pad inside each fuse holder, again for domestic all items should be now type tested, so consumer unit, not a fuse box, but also there is no retrospective requirement, some mark it as a fault, others will not, there was a code does not comply with current regulations, but that was removed, however the electrical safety council best practice guide last time I looked allowed one to simply fit labels where lights pre 1966 have no earth wires, as long as all class II items used, to my mind owners have had 50 years to upgrade, by now it should be a fail.
The big question is what do you want from the report?
1) Is the property as safe now as it was when last rewired.
2) Does the property comply with current regulations.
3) Is it safe for me to carry on using.
4) How much will it cost to upgrade.
5) Is it safe enough to rent out.
6) How much can I ask to be taken off house price to cover upgrade.
The list goes on, and depending on what you want, it will affect how deep the testing and inspection goes, this house has USB sockets and wifi sockets and light switches which for a full test all need removing, I would simply test lives to earth, but if a full test is requested it would be expensive as all these sockets need removing and refitting.
So how long is a piece of string, OK answer is one cable length, as the string runs down centre of cable, but clearly it could be shorter. I would not expect to take more than a day with a house so one days wages for a tradesmen is about right.