For simplicity put junit.jar from the lib directory into a new empty directory.
Put this code into a file named FractionTest.java in that same directory:
import junit.framework.TestCase;
public class FractionTest extends TestCase {
public void testAddition() {
Fraction half = new Fraction(1, 2);
Fraction fourth = new Fraction(1, 4);
Fraction actual = half.add(fourth);
Fraction expected = new Fraction(3, 4);
assertEquals(expected, actual);
}
}
Compiling:
$ javac -classpath junit.jar FractionTest.java
Running:
$ java -classpath .:junit.jar junit.swingui.TestRunner FractionTest