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Assignment 9: Testing and Refactoring

Due at Saturday, July 11th, 23:59

Task 21: White-Box Testing

3 points

We put a small Project called A9T21_DiscountTrouble in your repository. It consists of an Item class with static methods for calculating the sum of the item's prices (for example movies), including discounts.

You can find a Junit Test for this class, too.

  • What kinds of coverage does this test achieve?
  • Find all paths through the code and implement a JUnit assertion for each one.1) You can reuse the existing tests.

Task 22: Black-Box Testing

3 points
  • Image you have to test a class, whose source code you do not know.
  • The class's only public method is calculateDistance(double x1,double y1,double x2,double y2) and it is supposed to calculate the distance of two points in 2d.
  • Find and write down criteria for equivalence classes of test cases for a black box test of this class.
  • Write down a short justification why your criteria are good.

Task 23: Refactoring

6 points (+ 2 optional points)

We have an implementation of a class Rectangle that stores its coordinates in two instances of the class Interval, one for the horizontal and one for the vertical extension of the Rectangle.

  1. Review the code below. Give us six ideas how to improve it. If you can name a bad smell somewhere, do it. Which refactorings would you apply? We won't count the suggestion to introduce getter-methods. (Maybe you understand later why (see 3)).
  2. Give us for four cases the code that we would get after your refactoring.
  3. Optional! Reviewing your code after executing the refactorings, could you imagine why we suggest being reluctant concerning the introduction of getter-methods?

You can find the source code for this task (with a JUnit-test) as well in your repository in the project A09T23_Refactoring.

package gui;
import model.Rectangle;

public class View {
  public Rectangle rectangle;
  public void redraw() {

package model;
import static java.lang.Math.*;
import gui.View;

public class Rectangle {

  private Interval horizontal;
  private Interval vertical;
  private View view;

  public Rectangle(View view, int startX, int startY, int endX, int endY) {
    if ((startX > endX) || (startY > endY))
      throw new IllegalArgumentException("Parameters in wrong order.");
    this.horizontal = new Interval(startX, endX);
    this.vertical = new Interval(startY, endY);
    this.view = view; view.rectangle = this;

   * Create an empty Rectangle with no location.
  public Rectangle(View view) {
    this.horizontal = null;
    this.vertical = null;
    this.view = view; view.rectangle = this;
  public Vertex getCenter() {
    if (horizontal == null)
      return null;
    return new Vertex((horizontal.start + horizontal.end) / 2,
        (vertical.start + vertical.end) / 2);

  public boolean contains(Rectangle parameter) {
    if (parameter.horizontal == null)
      return false;
    if (horizontal == null)
      return false;
    // check whether the horizontal interval
    // contains the horizontal interval
    // in the other rectangle
    // AND
    // check whether the vertical interval
    // contains the vertical interval
    // in the other rectangle
    return ((horizontal.start <= parameter.horizontal.start) 
      && (parameter.horizontal.end <= horizontal.end))
      && ((vertical.start <= parameter.vertical.start) 
      && (parameter.vertical.end <= vertical.end));

   * Enlarge the Rectangle just enough so that it contains the other
   * Rectangle. If the Rectangle was empty it gets the same extension
   * as the other Rectangle.
  public void accommodate(Rectangle other) {
    if ((other == null) || (other.horizontal == null))
    if (horizontal == null) {
      horizontal = new Interval(other.horizontal);
      vertical = new Interval(other.vertical);
    horizontal.start = min(other.horizontal.start, horizontal.start);
    horizontal.end = max(other.horizontal.end, horizontal.end);
    vertical.start = min(other.vertical.start, vertical.start);
    vertical.end = max(other.vertical.end, vertical.end);

  public boolean equals(Object obj) {
    if (!(obj instanceof Rectangle))
      return false;
    Rectangle other = (Rectangle) obj;
    if (horizontal == null)
      return (other.horizontal == null);
    return (horizontal.equals(other.horizontal))
        && (vertical.equals(other.vertical));

  public String toString() {
    return "Rectangle(" + horizontal + " x " + vertical + ")";

The automated refactorings in Eclipse are more effective if you use some tricks:

  • Before extracting a method extract those expression you want to become parameters into local variables.
  • Before moving a part of a method to another class, you should extract this part into an own method in the current class.
  • If you need more tips: Ask on the mailing list! :-)

thus achieving full path coverage
teaching/lectures/oosc/2009/assignment_9.txt · Last modified: 2018/05/09 01:59 (external edit)

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