Zombie2Test.java

public class Zombie implements Compares<Zombie>

... remainder of Zombie code is unchanged

public class Zombie2Test {

    Zombie walker = new Zombie(WALKER);
    Zombie fatty  = new Zombie(FATTY);

    @Test
    public void shouldUseCompareMethods() {
        assertTrue(walker.isLessThan(fatty));
        assertTrue(fatty.isGreaterThan(walker));
        assertTrue(fatty.isEqual(fatty));
    }
}