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 Testing

h2.  1. Writing Simple Java Classes \(45 min\)

*First steps:

This class is not very interesting because we cannot

 do much with it.  However, it is

9. To create a new instance of an AreaCalc , type the following in the Interactions pane:

{code

}AreaCalc calc = new AreaCalc();{code}

To "ask" the AreaCalc object calc to compute the area of a 4 by 5 rectangle, type in

{code

}calc.rectArea(4, 5){code}

11. Experiment with using the object calc to compute the area of a few rectangles of different sizes.

12. How do you instantiate another AreaCalc and name it robot?

*Computing the area of a right triangle

*

Suppose you want to compute the area of a right triangle given its base and its height

.  What code should you write?  You basically have two options.

13. Write another class called AreaCalc2 with a method to compute the area of a right triangle given as input parameters the base and the height.

14. Add a method to class AreaCalc to compute the area of a right triangle given as input parameters the base and the height.

Now, suppose now you are asked to compute the area of a circle.  What approach would you choose?  What are the pros and cons of each of the possible approaches?

*Creating classes with fields

*

The following are classes with fields similar to class Entry discussed in lecture #18.

15. Write a class called Rectangle that has two double fields, width and height, and a method to compute the area.

16. Write a class called RightTriangle that has two double fields, base and height, and a method to compute the area.

17. Write a class called Circle that has one double field, radius, and a method to compute the area

.

h2.  2. Unit Testing with JUnit \(35 min\)

Extreme Programming \(XP\) is a software development methodology that is "very hot" these days and is currently embraced by the software industry.  One key element of XP, called "unit testing", is the idea of writing test code for

 functions \(or procedures or object methods\) before the functions \(or procedures or object methods\) are even written.  \(Don't ask me how to write test code for the test code themselves!  The whole thing is "kinda" suspiciously recursive with no well-defined base cases.\)

 
 
_The test code becomes in effect the "documentation and specification" of the behavior of the functions \(or procedures or object methods\) in code form!

_

Each time a function \(or procedure or object method\) is modified, it must pass its existing test code.  Each time a test code for a function \(or procedure or object method\) is modified, the corresponding

 function \(or procedure or object method\) may have to be revised to satisfy the new specification.

[JUnit

|http:-www.junit.org

] \(www.junit.org\) is an open source framework developed to support the above concept of unit testing for Java programs.  This tutorial will lead you through a simple example of how to write unit test code in developing a \(simple\) Java program with only one class.

*Step 0.

*

Run DrJava with Elementary Language level.  We will do all development in DrJava since it has very nicely integrated JUnit with its development environment.

 

*Step 1.

*

Suppose we want to model the notion of a smart person who knows his/her birthday and can compute the number of months till his/her next birthday given the current month.  For our purpose, a month can simply be represented by an integer, which in Java  is called int.  We start by writing "stub" code for the class Person  that is to represent our smart person.

{code

}   
class Person {

    /**
    * Computes the number of months till the next birthday given the current month.
    */
    int nMonthTillBD(int currentMonth) {
        // to do
    }

}
{code}

Notice in the above there is really no concrete code.  As a matter of fact, the above would not compile.  Now we must abandon everything and start writing test code for nMonthTillBD\(...\).

 

*Step 2.

*

DrJava is very nice to you and will create a test stub class for you if you know what to click:

  
* Go to the File menu and select New Junit Test Case...

* Create a stub test case called Test_Person.  DrJava will create a stub class that looks like the following

{code

}
/**
 * A JUnit test case class.
 * Every method starting with the word "test" will be called when running
 * the test with JUnit.
 */
class Test_Person extends TestCase {
    /**
     * A test method.
     * (Replace "X" with a name describing the test.  You may write as
     * many "testSomething" methods in this class as you wish, and each
     * one will be called when running JUnit over this class.)
     */
    void testX() {
    }
}
{code}

At this point, do not worry about what "extends TestCase" means in the above.  DrJava is re-using the class TestCase from the JUnit framework in some clever way without you having to deal with all the details of how to use an existing class from some other files.

* Compile this test class only \(by clicking on Tools/Compile current document\), and save the class in the same directory as Person.  The Test_Person class should compile, though the Person class does not.

* Change the name of the stub method testX\(\) in the above to test_nMonthTillBD\(\)and add code  to make it look like the code below.

{code

}
class Test_Person extends TestCase {

    void test_nMonthTillBD() {

        Person peter = new Person(9); // a person born in September.

        assertEquals("Calling nMonthTillBD(2).", 7, peter.nMonthTillBD(2));
        assertEquals("Calling nMonthTillBD(9).", 0, peter.nMonthTillBD(9));
        assertEquals("Calling nMonthTillBD(12).", 9, peter.nMonthTillBD(12));
    }
} 

{code}
Note that in the code for test_nMonthTillBD\(\), we have decided that we only need to know the birth month of a person in order to compute the number of months till the next birth day.  As a result, we instantiate a Person object by passing only the birth month: new Person\(9\).

  

Also the test covers three cases:

* the current month is less than the birth month

 
* the current month is equal to the birth month

* the current month is greater than the birth month.

The

 {code

assertEquals

{code}

*Step 4.

*

After you have cleaned up your code for Person as shown in the above, you should be able to compile Test_Person.  With Test_Person open, click on the Test button in DrJava tool bar.

What do you see?  Something has failed!  The formula for the number of months till the next birth day seems to be the culprit.  We will pretend ignorance and fix the "bug" in two steps.

*Step 5.1

*

Change the formula to

{code

}
    int nMonthTillBD(int currentMonth) {
        return _bMonth - currentMonth; // to do
    }
{code}
Compile all and test again.

Still we have errors.

*Step 5.2

*

Change the formula to

{code

}
    int nMonthTillBD(int currentMonth) {
        return (_bMonth - currentMonth + 12) % 12; // to do
    }
{code}

Compile all and test again.  Now everything should pass!  You may now remove the TO DO comment from the code of nMonthTillBD.

In XP programming, only after a method has passed its unit test that you are allowed to proceed to another one

.

h2.  3. Additional Reading:

Lecture notes on Object-Oriented Programming using Java by Dung X. Nguyen and Stephen B. Wong: http://cnx.org/content/col10213/latest

 
Here is another link for a more detailed discussion of JUnit testing uisng  DrJava: http://cnx.rice.edu/content/m11707/latest/

The following link contains a more elaborate discussion on JUnit testting and a more involved example of testing:  http://junit.sourceforge.net/doc/testinfected/testing.htm

.


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