Nasao sam ti ovaj (srpska cirillica i engleska latinica) http://www.srpskibre.com I ovaj http://www.srpskijezik.rs

Up to now I have not found one yet :( There is this one which I have never used http://serbianlesson.com/ and this one - which I like - but it is more for learning vocabulary http://www.goethe-verlag.com/tests/index1.htm

http://www.srpskibre.com/sr/exercise/v4.php, http://www.srpskibre.com/sr/grammar/nominativ.php , https://sites.google.com/site/srpskijezikiknjizevnost/vezbe-za-srpski-jezik/zadaci-za-vezbane-iz-srpskog-jezika Surf these sites, they could maybe help you. Good luck ! K.