	CS 535 Object-Oriented Programming & Design Fall Semester, 2001 Object, Debugging, Testing
	Previous Lecture Notes Index Next © 2001, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 27-Sep-01

Contents of Doc 7, Object, Debugging, Testing

References
VisualWorks Application Developer’s Guide, doc/vwadg.pdf in the VisualWorks installation. Chapter 9 Debugging Techniques .

Reading
VisualWorks Application Developer’s Guide, chapter 9 Debugging Techniques

Or

Joy of Smalltalk, Ivan Tomek, chapter 3 pages 96-99


Doc 7, Object, Debugging, Testing Slide # 2

For more Information on:
Numbers

Read Joy of Smalltalk, chapter 5

Control Structures

Read Joy of Smalltalk, chapter 5


Doc 7, Object, Debugging, Testing Slide # 3

Object

All 'things' in Smalltalk are objects

Objects are created from classes

The class Object is the parent class of all classes

Object class contains common methods for all objects

Determines behavior for all objects


Doc 7, Object, Debugging, Testing Slide # 4

Some Important Behavior Defined in Object
printString


Returns a string representation of the receiver
Similar to toString in Java

isNil, notNil

Tests to see if the receiver has been initialized or is still nil

\| a \|	Result printed
Transcript
clear;
print: a isNil;	true
cr;
show: a printString;	'nil'
cr;
print: a class;	UndefinedObject
cr.
a := 5.
Transcript
print: a isNil;	false
cr;
show: a printString;	5
cr;
print: a	5
cr;

When the above code is compiled the compiler notices that a is used before it is assigned a value. The compiler will ask you if want use a before it is assigned.


Doc 7, Object, Debugging, Testing Slide # 5

printString
Since implemented in Object all objects inherit the method

printString is sent to an object when

Expression is evaluated with "Print it"
When the object is displayed in some VW windows
When sent to the Transcript via print:

printString uses printOn:

Object>>printString
   "Answer a String whose characters are a description of the receiver."
   | aStream |
   aStream := WriteStream on: (String new: 16).
   self printOn: aStream.
   ^aStream contents


Doc 7, Object, Debugging, Testing Slide # 6

Overriding Default printString Behavior
Implement printOn: not printString

printOn:'s argument is a stream

Stream Writing methods:

nextPutAll: aString
nextPut: aCharacter
print: anObject
cr
space
tab
crtab


Doc 7, Object, Debugging, Testing Slide # 7

Example

Smalltalk.CS535 defineClass: #Counter
   superclass: #{Core.Object}
   indexedType: #none
   private: false
   instanceVariableNames: 'count '
   classInstanceVariableNames: ''
   imports: ''
   category: 'Course-Examples'

CS535.Counter class methodsFor: 'instance creation'

new
   ^super new initialize

CS535.Counter class methodsFor: 'examples'

example
   "Counter  example"
   | a |
   a := Counter new.
   a
      increase;
      increase.
   ^a count


Doc 7, Object, Debugging, Testing Slide # 8

CS535.Counter methodsFor: 'accessing'

count
   ^count

decrease
   count := count - 1

increase
   count := count + 1

CS535.Counter methodsFor: 'initialize'

initialize 
   count := 0

CS535.Counter methodsFor: 'printing'

printOn: aStream
   aStream
      nextPutAll: 'Counter(';
      print: count;
      nextPutAll: ')'


Doc 7, Object, Debugging, Testing Slide # 9

Equality

All objects are allocated on the heap

Variables are references (like a pointer) to objects

A == B

Returns true if the two variables point to the same location

A = B

Returns true if the two variables point to equivalent objects
In Smalltalk you want to use '=' nearly all the time

A ~= B

Means (A = B) not

A ~~ B

Means (A == B) not
Doc 7, Object, Debugging, Testing Slide # 10

Equality Example - Counter

| a b |
a := SimpleCircle origin: (0 @ 0) radius: 1.
b := a.

Now a == b and a= b are both true

a := SimpleCircle origin: (0 @ 0) radius: 1.
b := SimpleCircle origin: (2 @ 5) radius: 3.

Now a == b and a= b are both false

a := SimpleCircle origin: (0 @ 0) radius: 1.
b := SimpleCircle origin: (0 @ 0) radius: 1..

Now a == b is false

Should a = b be true or false?


Doc 7, Object, Debugging, Testing Slide # 11

Defining the Meaning of =
Object

Does not know what ='s means for your class
Default definition is to use ==

If you override = also override #hash


Doc 7, Object, Debugging, Testing Slide # 12

SimpleCircle Example
CS535.SimpleCircle methodsFor: 'comparing'

= aCircle
   ^(origin = aCircle origin) & (radius = aCircle radius)

hash
   ^origin hash + radius hash

Comparing floats for equality is dangerous

This is not a great hash function, but works as an example


Doc 7, Object, Debugging, Testing Slide # 13

Debugging
Ways debugger is called by

Executing code in workspace using "Debug it"
Executing "self halt"
An error raised in your code

To illustrate how the debugger works we will go through an example


Doc 7, Object, Debugging, Testing Slide # 14

Code for Debugging Example

Smalltalk.CS535 defineClass: #Counter
   superclass: #{Core.Object}
   indexedType: #none
   private: false
   instanceVariableNames: 'count '
   classInstanceVariableNames: ''
   imports: ''
   category: 'Course-Examples'

Class method

new
   ^super new initialize

Instance Methods

count
   ^count

decrease
   self increment: 1      "Note the error"

increase
   self increment: 1

increment: anInteger
   self halt.
   count := count + anInteger

initialize 
   count := 0


Doc 7, Object, Debugging, Testing Slide # 15

Sample Test code in Workspace
Execute the following code with "Do it"

| count |
count := Counter new.
count
   decrease;
   decrease;
   increase.

When the statement "self halt" is executed you will see a window like:


Doc 7, Object, Debugging, Testing Slide # 16

When you click on the debug button, you get the debugger. The debugger looks like:

Debugger Components Execution Stack Pane

Lists the methods calls that are on the execution stack. Selecting any of the listed method calls shows the state and code for the method

Code Pane

Shoes the source code of the selected method. You can make changes to the code shown. To make changes just edit the code and accept the changes. When you run the code, it starts from the selected method with the new changes


Doc 7, Object, Debugging, Testing Slide # 17

Instance Variable List Pane

This pane lists all the instance variables in the receiver of the method selected in the execution stack pane. Selecting an instance variable will show its current value in the instance variable value pane.

Instance Variable Value Pane

Displays the value of the selected instance variable. By editing this pane you can change the value of the instance variable. Just type in the new value or code that will return the new value and accept the changes.

Local Variable List Pane

This pane lists all the local variables in the method selected in the execution stack pane. Selecting a local variable will show its current value in the local variable value pane.

Local Variable Value Pane

Displays the value of the selected local variable. By editing this pane you can change the value of the local variable. Just type in the new value or code that will return the new value and accept the changes.

Step Button

Executes the currently selected message in the Code pane

Send Button

Calls the currently selected message in the code pane and shows the code for the method. Allows you to step through this method.

For more information on using the Debugger see Chapter 9 Debugging Techniques of the VisualWorks Application Developer's Guide.


Doc 7, Object, Debugging, Testing Slide # 18

Testing

Johnson's Law

If it is not tested it does not work

Types of tests

Unit Tests

Tests individual code segments

Functional Tests

Test functionality of an application


Doc 7, Object, Debugging, Testing Slide # 19

Why Unit Testing

If it is not tested it does not work

The more time between coding and testing

More effort is needed to write tests
More effort is needed to find bugs
Fewer bugs are found
Time is wasted working with buggy code
Development time increases
Quality decreases

Without unit tests

Code integration is a nightmare
Changing code is a nightmare


Doc 7, Object, Debugging, Testing Slide # 20

Unit Tests Must be Easy To Run
Must be able to

Easily run many tests at once
Allow others to run the tests
Keep the tests for later
Scale with more developer and project size

Test stored in a workspace

Do not work in any sizable project
Do not work well with multiple programmers
Are easily lost
Are not run very often


Doc 7, Object, Debugging, Testing Slide # 21

Testing First

First write the tests

Then write the code to be tested

Writing tests first:

Removes temptation to skip tests

Makes you define of the interface & functionality of the code before


Doc 7, Object, Debugging, Testing Slide # 22

SUnit

Testing framework for automating running of unit tests in Smalltalk

In SUnit

Programmer manually writes the test
SUnit automates the running of the test
Simplifies finding tests that fail

Ports to other languages can be found at:

http://www.xProgramming.com/software.htm


Doc 7, Object, Debugging, Testing Slide # 23

How to Use SUnit
1. Make test class a subclass of TestCase

   Smalltalk.CS535 defineClass: #TestCounter
   superclass: #{XProgramming.SUnit.TestCase}
   indexedType: #none
   private: false
   instanceVariableNames: ''
   classInstanceVariableNames: ''
   imports: ''
   category: 'Course-Examples'

You do not have to remember the full name of TestCase. Just use the name TestCase and it will be expand the full name for you.

2. Make test methods


The framework treats methods starting with 'test' as test methods

testIncrease
| aCounter |
aCounter := Counter new.
self assert: aCounter count = 0.

aCounter increase.
self assert: aCounter count = 1.


Doc 7, Object, Debugging, Testing Slide # 24

How to Use SUnit 3. Start TestRunner

   TestRunner open

4. Select test class and click on "Run"

The list pane between Refresh and Run contains a list of all the Test classes in the system. Select the test class you wish to run. The click on the run button. If all tests work, then the middle panel will turn green. If some of them fail, then the middle panel will turn red. The list pane on the bottom of the window will list all tests that failed. Select one and click on the Debug button to open the debugger on the test method that failed.

Note VisualWorks ships with a number of test classes in the image. When working on a project I remove them. Then all the test classes in the image are for my project. I then always click on the RunAll button to run all the tests. Sometimes when you change a method, you break code that uses that method. Running all the tests uncovers those problems early.


Doc 7, Object, Debugging, Testing Slide # 25

TestCase methods of interest

Methods to assert conditions:

   assert: aBooleanExpression
   deny: aBooleanExpression
   should: [aBooleanExpression]
   should: [aBooleanExpression] raise: AnExceptionClass
   shouldnt: [aBooleanExpression]
   shouldnt: [aBooleanExpression] raise: AnExceptionClass
   signalFailure: aString
setUp

Called before running each test method in the class.
Used to: Open files Open database connections Create objects needed for test methods

tearDown

Called after running each test method in the class.

Used to: Close files Close database connections Nil out references to objects


Doc 7, Object, Debugging, Testing Slide # 26

More Test Examples to Show Syntax

Smalltalk.CS535 defineClass: #TestCounter
   superclass: #{XProgramming.SUnit.TestCase}
   indexedType: #none
   private: false
   instanceVariableNames: 'counter '
   classInstanceVariableNames: ''
   imports: ''
   category: 'Course-Examples'

CS535.TestCounter methodsFor: 'testing'

setUp
   counter := Counter new.

tearDown
   counter := nil.

testDecrease
   counter decrease.
   self assert: counter count = -1.

testDecreaseWithShould
   "Just an example to show should: syntax"
   counter decrease.
   self should: [counter count = -1].

testIncrease
   self deny: counter isNil.
   counter increase.
   self assert: counter count = 1.

testZeroDivide
   "Just an example to show should:raise: syntax"
   self 
      should: [1/0]
      raise: ZeroDivide.
   
   self 
      shouldnt: [1/2]
      raise: ZeroDivide

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