The only boiler test in which I would have any confidence is one that I had witnessed.
I once purchased a 3"Burrell from a dealer who provided a new commercial certtificate . On stripping it down for a re paint I found a wooden plug in one of the safety valves and a section of steel angle undet the front of the smoke box!. After some discussiona suitable discount was arranged and a replacement boiler ordered.
The 20 week delay at least gave me time to do the re paint . I was given the option of either having the boiler delivered to the Foss Way show or, the makers prefered choice , collecting it from Exeter to see it on test .
After a 180 mile drive I arrived to find the boiler on test at 1 1/2 WP. . It was then pumped up to 2 WP with the comment " let's leave it at that while we have a drink and I go through the paperwork with you"
1/2 hr later the paper towel under the boiler was still dry and I was given some more to wipe over the boiler "To satisfy yourself that it is OK. "
The boiler was thern carried to the car with the comment " I will carry it for you . If you drop it after that you will have to bring it all the way back for me to sort out"
First class service and a very well made boiler .