You need to write a class with less than 10 lines. Here is a nice example provided in the article "Writing a JUnit Test in 5 minutes" by Kamal Mettananda with some minor changes:
package com.parcelhouse.myproj;
public class Calc {
public int add(int a, int b) {
// errorneous method
return a+b+1;
}
public int multiply(int a, int b) {
return a*b;
}
}