If it helps you I can also give my experience of FI test day.
The test is broken down into sections. You have the long brief, short brief, questions and answers and the flying test.
You will normally be given a subject to cover on your long brief, and given ample time to prepare for it. On my test I got stalling. The short briefing is the lesson that you will teach in the aeroplane, I had PFL's, which was handy because doing a PFL during the test is mandatory as in demonstrating a spin. The question and answer session lasted about an hour for me. The examier can ask you anything from the PPL syllabus, so it is important that you know you stuff. However, if you don't know the answer, its no big deal, you just need to know where to locate the information.
The flying test is pretty straight forward. Even though the main body of the test is what you have briefed for your short briefing, the examier will ask you to demo or teach other aspects. For example on the climb out from the airport I was asked to start teaching the climb.
I think you will find the test fairly relaxed and most likely quite enjoyable, until you have to write out the cheque to pay for it at the end
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Instructing is a very rewarding job, enjoy it, its a lot of fun. I have been flying a while now, and I still enjoy it.
All the best with the course and test.