As Sadhna pointed out , there are couple of tests at Skill-Guru , all of them free and one paid
Free SCJP 5 Mock test
Free SCJP 6 Mock test
SCJP 6 Mock test
Now the free tests do not come with explanation so you can practice but might not understand what mistake you did.
The paid test priced at $1.99 has 125 questions and has explanation for each and every question. This will help you to understand your mistakes.
And even $1.99 comes back with money back guarantee.
So the choice is in your hands.
Good luck with your preparations.