It took me 2, I failed my first one within the first few minutes (and I knew I'd failed there and then because the instructor had to use his set of brakes... even though it was completely unnecessary imo
but anyway) it was awful having to continue for the rest of the test when I just wanted to get out the car and cry
Loads of people fail first time though and honestly it made me so much more confident and determined for the second time so don't worry about it too much if you do fail. I actually think that failing a driving test isn't so much down to how good you are at driving (you wouldn't be put in for it if you weren't capable), it's more down to nerves and stress getting the better of you.