Firstly, congratulations.
As far as I remember, the reactions test is the one where you're sat at a computer with some headphones, pedals & specially made keyboard with different colour buttons. The screen tells you which buttons/pedals to press, and you have to keep up.
A tip: It runs 2 programmes. One is the pace set by the computer, so if it's going too fast, don't be afraid to stop for a few seconds & let it get back to your pace. The other is set by you. Try getting into a rythm a maintaining it, getting as many correct as possible.
The interview could be a number of pre-approved questions, but is usally competency based (ie emergency situation, working alone etc). You may be given a form to fill in with these questions on already, so if you decided to "bend the truth", remember what you wrote.
It's also very likely that the interviewer will ask you to elobroate or provide another example if they don't feel it's good enough. This is where you need to decide if you feel the example you gave is good enough (tell them), or if you are going to give them another one, make sure it's relevant.
Hope this helps. Best of luck.