private void addStudent(StudentDirectory dir2, int i) {
String id = "" + i;
Student student = new Student(id);
student.setId(id);
student.addCredits(i);
dir.add(student);
}
private void verifyStudentLookup(StudentDirectory dir, int i) {
String id = "" + i;
Student student = dir.findById(id);
assertEquals(id, student.getId());
assertEquals(id, student.getLastName());
assertEquals(i, student.getCredits());
}