Don't worry, it's will probably be the biggest anticlimax you've ever experienced in your whole life.
The assessor will pontificate and waffle on and on until he finally asks you a question like " there are 3 types of electrical fault, what are they?' this will throw you at first, as you try to pull yourself out of the stupor he's hypnotised you into, with his blah blah blah blandness and out of blind panic you may answer "short crust, earth fault and would you like another biscuit overlord". But dont worry, he will then take over the conversation and waffle on and on about something else before asking such searching questions like "what size earthing conductor should be used in a TNC-S system" or "what size bonding conductor blah blah blah" etc etc........you'll try to answer but dont worry he likes the sound of his own voice, so leave the room (mentally that is, dont actually walk out) and just nod at 5 second intervals.
Once he's checked you've spent the required amount of money on all the useless books and other crap, its onto the job. But lets face it, he wont find anything wrong will he (unless your a pillock) as you've spent god knows how much time and money making it perfect, and researching on forums like this, so it should be a "proper job". Anyway, even if it isn't he'll probably be easily fooled into missing the obvious mistake by quickly asking him a distracting question about something he likes eg, Part P, electricity, money, women's knickers/mens pants etc
Its then onto the testing (but dont forget he's running out of time and interest by now). So plug your tester into the socket and try to press the correct button.......
You cant fail, not unless your a buffoon, they want your money its that simple