CPE 102 Program 1a - SUnit, A Simple Unit Testing Class

Ground Rules

No collaboration is allowed on this program assignment. Your program must be an individual and original effort. Except for any situations explicitly identified in this assignment, if any, you may only receive help from your instructor or the tutors provided by the Computer Science Department. See the Syllabus for the significant consequences for disallowed collaboration and/or plagiarism.


None so far - updates and corrections, if any, will show up here (be sure to refresh this page as necessary).

Due Date and Submission Instructions

Submit the following file(s) on one of the CSL servers using handin as follows:

    file(s): SUnit.java

    touser: eaugusti

    assignment/subdirectory: 102-program01a

Orientation and Sample Code

Unit testing and Test Driven Development are widely used techniques to help ensure code quality. They can be especially helpful to beginning programmers because their use encourages and facilitates incremental development. Incremental development helps you learn-as-you-go and can minimize confusion, bugs, and the amount of code that needs to be rewritten. While these techniques may not save time, they have been shown to improve code quality when employed by experienced professionals. It is my belief, when used correctly, their use will save most beginning programmers much time and frustration, and contribute to a deeper understanding of the process of software development.

There are many unit testing frameworks already in existence. They tend to be rich, complicated environments that can easily overwhelm beginning programmers and distract attention away from the more fundamental skills that need to be mastered first. This assignment attempts to solve that conundrum by having you write a small, but useful, subset of unit testing functions. By writing them yourself you will have a deeper understanding of what they are doing and how they work. Also, because they are relatively simple, they are serve as excellent place to start learning Object Oriented Programming techniques! This assignment is modeled after a small subset of methods found in the JUnit framework.

Unit testing is not really an "object oriented" problem but, since this class is an OOP class and we are using Java, we'll have to make it fit. Normally I'd would avoid problems using the static key word as long as possible but, due to the nature of the problem, we are going to dive in head first! In Java methods (a.k.a. functions) can be static. The nice thing about static methods is they can be called without having to construct an object. The only restriction on static methods is that can only use static data and local variables (not instance variables). This is not a problem for us since we don't need any other type of data for our unit testing methods. When writing static methods you simply include the static keyword in the method declaration as follows:

    public class SUnit
       // Class variables here - syntax shown below.

       public static void assertEquals(long expect, long actual)
          // Stuff not shown...


The SUnit class will keep track of how many tests have been run and how many of them detected errors. This means it will need some variables that live for the life of the program and not just during a single method call. This means local variables will not sufficient. Normally we would declare instance variables (variables declared in a class and outside of a method. However, static methods can't access instance variables because no instance (object) was created and, therefore, they don't exist! The solution is to declare class variables. A class variable belongs to the class and is shared by all instances of the class and it exists for the life of the program. It is very much like a global variable in C (if you know what that is). Fortunately, class variables can be accessed by static methods - perfect for out needs. Class variables are declared in a class and outside of a method and include the static keyword in the declaration. Here is an example of how you would declare a class variable in SUnit:

      public class SUnit
         private static int testCount;

         // Methods here...


Calling static methods is straightforward in Java. Since a static method belongs to the class you simple call it as follows:

      SUnit.assertEquals(x, y);

Finally, you will be making use of the Java Standard Library's Throwable class, specifically it's printStackTrace method when reporting errors. To use the method you must first construct a Throwable object and then call it on the object instance you just created.  The Throwable class has a constructor that accepts a message - this is how you will provide the exact message specified later in this assignment. Here is an example of how you could construct a Throwable object and call the printStackTrace method:

      Throwable throwable = new Throwable("Your error message here");

  1. To receive full credit your source code must meet the Programming Guidelines.

  2. To receive any credit your solution must pass all test of the provided test driver (link and instruction provided below) when compiled and run on any of the CSL servers.

  3. Implement a class called SUnit to this specification. Your solution must only have the public methods specified in the specification. Note that there is no main and no explicit (written) constructor.

  4. You may only use two private static int class variables, one to keep track of how many assert methods are called and the other to keep track of how many assert methods reported a failure. No other data fields are allowed in the class. You may use as many local variables as you deem necessary.

  1. Start early, read the entire assignment, and ask your instructor for any necessary clarifications before writing any code!
  2. Develop incrementally, one method at a time, testing as you go.  The methods are very similar so developing and testing one well and then using it as a model for the others will be both more efficient and more pleasant.

Testing With the Provided Test Driver
  1. You should develop and use your own tests prior to using the provided test driver.
  2. Do not use the provided test driver (provided on the first due date for the assignment, not before) until your solution is complete and you believe it is correct.

  3. Using the save-as feature of your browser, not cut-and-paste, save SUnitTest.java in the same directory as your SUnit.java file. Note that SUnitTest.java will be published on the morning of the first due date - it is not published earlier to encourage you to develop your own tests!

  4. Compile both SUnitTest.java and SUnit.java and run SUnitTest (see How to Compile and Run From the Command Line, as necessary). Remember that your code will be graded on one of the CSL servers so, to avoid unpleasant grading surprises, be sure to test on any one of those machines at least once after all changes and just before handing in!

Program courtesy of Kurt Mammen.