thanks-
worry is a good thing as it will keep you motivated !
my advice is that you obviously must know how to test and what your readings mean.
basic stuff that should be in your head anyway- brian scaddan has a very good book about 17th edition testing this helped me a lot to refresh my mind- basic figures and calculations on the testing side zs=ze+r1=r2 etc - what is r1,r2 - bonding, where is zone 0, zone 1 in bathroom - rule of thumb x0.8 on tabulated zs values etc- you just need to be competent at testing- you need the green regs and up to date books.
you also need to show your tester reads correct - i have a transmille 2080 calibration checker and a proving unit so he liked this,
so read up on your guidance notes 3, on site guide and know where to find stuff you might need in them.
the most important thing is lots of coffee and nice posh big cookies lol.
niceic are not monsters and try to trip you up, they just want to know that you are competent- as for checking works you have done- if you have problems with this then talk to him - not everything is set in stone- and i am sure they will try and find the best way to accomodate you- remember they want your custom and to get their numbers up- you will be fine