Testing Your Code

Developers are also Testers

Up to this point in the class we’ve had various automated grading tools available to test our code and make sure it works correctly. However, it is important to understand that these buttons are just running code written by other developers (in this case, the instructors of the course), and these tests can have the same limitations as any other program. For example, it is often impossible to guarantee that these tests will accurately test all possible inputs or reach 100% code coverage. Likewise, depending on how the solution is written, the edge cases and boundary conditions may be different than the ones that were originally used for testing.

At this point, we have learned enough programming syntax and terminology to start running our programs manually and developing our own tests. So, from this point forward, many of the projects will not give us access to the full automated grading process before we submit it. In effect, it is now our job to properly test our program using various inputs, both the ones provided and ones that we develop ourselves, in order to be sure that it is working properly.

After we submit the project, the full autograder will still be used to grade our work. The autograder will confirm that your project matches the specification within a reasonable limit. However, we won’t be able to go back in and make any changes after we submit the project. So, we’ll have to be extra careful and make sure our programs are fully tested before we submit them.

Write a test Method

One thing that we can do is add an explicit test method to any class in our program. Our test method may contain any code needed to test our program. We are always allowed to add additional methods to any class as needed - we won’t be penalized for that in grading.

For example, we could add a test method to the previous example to test some of the functions:

import java.lang.Math;

public class Dry{

    public static void main(String[] args){
        quadratic(1, 0, -4);
        quadratic(2, 7, 3);
    }

    public static void quadratic(int a, int b, int c){
        d = discriminant(a, b, c);
        rootOne = (-b - Math.sqrt(d)) / (2 * a);
        rootTwo = (-b + Math.sqrt(d)) / (2 * a);
        System.out.println(rootOne);
        System.out.println(rootTwo);
    }

    public static int discriminant(int a, int b, int c){
        return b * b - 4 * a * c;
    }

    public static void test(){
        int answer1 = discriminant(1, 3, 1);
        System.out.println("Answer 1 was " + answer1 + " and should be 5");
        int answer2 = discriminant(3, 3, 3);
        System.out.println("Answer 2 was " + answer1 + " and should be 27");
    }
}

In the method, we see that we are calling the discriminant method with a few different values. The expected answer values we see in the print statements can be manually calculated and verified using a calculator. It is important that we calculate these manually instead of relying on our program to calculate them - if we did, how would we ever know if it was actually incorrect?

Using a test Method

Once we’ve written a test method, we have to change our program so that it calls the method. The simplest way to do this is to just add that function call at the very top of the main() method:

    public static void main(String[] args){
        test();
        quadratic(1, 0, -4);
        quadratic(2, 7, 3);
    }

Since the test method may produce output or change the functionality of our program, it is always important to remember to REMOVE the test method from our main method before we submit the program.