The 25th International Olympiad in Informatics was held in Brisbane, Australia in 2013. There were two competition days, with 3 tasks given to the competitors on each day. You can see the tasks and test cases below.

Day 1:
      Dreaming
      Art Class
      Wombats

Day 2:
      Cave
      Robots
      Game

Other materials:
      Test cases
      Practice problems


Note that the grading model changed at IOI'94 and beyond.
Before IOI 1994, a human evaluator would sit behind the competitor's computer and do the testing manually (enter test data through the keyboard, check the output on the screen). Starting from IOI 1994, an automatic grading process is used, with test input defined in files.