It rather depends on the test. The Merlin had done about 1800hp in 1938? for the "speed Spitfire". A large number of engines have hit some rather high power levels for a few minutes at a time but passing a type test at those power levels or even a test to "OK" an "emergency" rating can be rather different. For example while the US limited WEP to 5 minutes in service the test engine had to survive 7 1/2 hours at that power level, 5 minutes at a time.
Please remember that the Vulture HAD passed a type test at 1845hp 3000rpm at 5,000ft and 1800hp for take-off at 3200rpm and we know how that turned out in service. Maybe the MK V would have been OK but just because an engine hits a power level on a test stand does not mean that engine can go into service at that rating. The P&W R-1340 (AT-6 engine) had hit over 900hp back in the early thirties for a few moments (and survived) but P&W never rated the engine at more than 600hp.