Unit Testing With println

Testing is a discipline in itself. (At some point you may find yourself taking Com S 417, Software Testing.) Determining whether a complex system is going to work correctly under all conditions is extremely difficult. In this course we will only focus on unit testing, which is where we test a single component (usually a class) all by itself to ensure that it conforms to its specification.

We have seen many examples of simple unit tests. As one example, consider the class Basketball. We saw this class back in lab 2; you can review the javadoc here. In order to test it, we start thinking about what should be true about a correctly implemented basketball:

For each such assertion we come up with, we can write a simple test case in which the actual value we get from calling a method is printed out, along with the correct or "expected" value we really should get. 
public class BasketballExample
{
  public static void main(String[] args)
  {
    Basketball b = new Basketball(5);
    
    // A newly constructed basketball should not be dribbleable
    System.out.println(b.isDribbleable());
    System.out.println("Expected: false");
    
    // A newly constructed basketball should have the diameter it was constructed with
    System.out.println(b.getDiameter());
    System.out.println("Expected: 5.0");
    
    // After inflating, the basketball should be dribbleable
    b.inflate();
    System.out.println(b.isDribbleable());
    System.out.println("Expected: true");
    
    // After inflating, the basketball should still have the diameter it was constructed with
    System.out.println(b.getDiameter());
    System.out.println("Expected: 5.0");
  }
}
If the Basketball class is implemented correctly, running this main method should produce the output: 
false
Expected: false
5.0
Expected: 5.0
true
Expected: true
5.0
Expected: 5.0

Using a test framework

With only four test cases, it is easy enough to look at the output and see whether the actual values match the expected values. The Basketball class is very simple. A more complex class may have dozens or hundreds of test cases, and it is tedious to have to read through the output to check for correct values.

Since we are programmers, we wonder: couldn't we just write a program to automatically check the test output? And (since we are programmers) of course the answer is yes! That is the idea of a test framework. Instead of using System.out.println, we write the test using a few special methods defined by the framework, and the framework completely automates the process of checking the results. In this course we use a framework called JUnit that extremely easy to use and is nicely integrated with Eclipse.