Testing Object-Oriented Software A Presentation at a DFW ASEE Meeting Dr. David C. Kung

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Testing Object-Oriented Software

A Presentation at a DFW ASEE Meeting

Dr. David C. KungThe University of Texas at Arlington

andAdvanced Software International Corporation

Arlington, Texas 76019-0015817-272-3785

[email protected]

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Overview of Presentation

• Why Object-Oriented Software Testing• The State-of-the-Research• OO Software Testing Research at UTA• OOTWorks Software Demonstration

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Why Object-Oriented Software Testing

• transition to OO development is not easy– OO conceptualization, design and programming

significantly impact the quality

– many developers’ mindset is still in procedural design and programming

– anti-design patterns are commonly found in OO design and OO code

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Case Study 1: Analysis of a Fedex Ship Manager Software

• This software was designed and implemented by a team of students taking an OO software engineering class

• It has nothing to do with Fedex

• The software was supposed to compute and display the shipment charges for all Fedex services from a given origin zip to a given destination zip

• This program is working but it has some design problems

• We show how OOTWorks can be used to detect these design problems

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Poor Conceptualization

NextAfternoon,OvernightExpress,Ground, etc. are services. They are not a RateChart.

It is better to use association.

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Poor Responsibility Assignment

There should not be a class called “RateCalculator”. The services are the “experts” who know how to calculate their own rates.

This design assigns the responsibility to the wrong object.

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Incorrect Use of Inheritance

Child classes must not repeat the same code as the parent class, failing to utilize the inheritance and polymorphism features. This increases the maintenance effort.

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Better Design

Better conceptualization.

The services use ZoneChart and Delivery Area Surcharge to calculate rates.

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Better Design

The subclasses inherit and use all of the methods of the superclass.

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Automatic Design Improvement The repeated code can be deleted from the subclasses.

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Automatic Design Improvement

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• OO features introduce new testing problems– encapsulation leading to long method invocation

chains, more difficulty to understand the (overall) functionality

– inheritance and polymorphism: which method to execute is determined at run time

– multiple and/or repeated inheritance may cause incorrect interaction in child classes

– you cannot test a class, you can only test instances of a class

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0

100

200

300

400

500

600

700

800

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Invocation chains in the InterViews Library: 122 classes, >400 relationships

Chain Length

Num

ber

of C

hain

s

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main () { Shape *p; …. p->print(); // which print() to // execute? … }

Shapeprint ()

Boxprint ()

Squareprint ()

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• objects engage in complex interdependent relationships– testing one object may require test stubs to simulate

other objects

– test stubs construction is costly and time consuming

– mutual or cyclic dependencies introduce additional complexity and costs in unit and integration testing

– need a test order for unit testing and integration testing


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Complex Relationships

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• objects exhibit strong state dependent behaviors– how to identify states and transitions?

– how to identify state dependent interactions?

– how to generate test cases to test state behaviors?

– how to reduce the complexity of state behavior testing?


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The State-of-the-Research

• OO software testing began in the 1990s• A number of test methods and techniques have

been proposed• There are various tools, some are free some are

not• The tester still has to do a lot of work

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The State-of-the-Research

• OO Test Methods and Techniques– incremental testing of class hierarchy

– test order

– object state testing

– class testing, cluster testing

– data flow analysis

– testing polymorphic relationships

– data flow analysis for exception handling mechanism

– OO regression testing

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OO Software Testing Research at UTA

• A reverse engineering technology• Plus a set of utilities to facilitate

• program understanding• design documentation • design analysis• design improvement • metrics calculation• test scheduling• change impact analysis• version comparison

• test case generation• test data generation • design improvement• code review & analysis• code improvement• test execution• result analysis• and more ...

• The result is the OOTWorks toolkit

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Why OOTWorks

• It improves productivity and quality in– Documentation

– Design and code reviews

– Testing, regression testing and maintenance

– Test planning and scheduling

• It reduces the time and effort required to prepare for CMM/ audit each year

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The OOTWorks Modules

ORD(Object Relation Diagram)

BBD

(Block Bench Diagram)

OSD(Object State Diagram) (Package Relation Diagram)

PRD

OID(Object Interaction Diagram)

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Object Relation Diagram (ORD)

• Visualization of– Classes, relationships, data members, function members,

and source code, selectable by the user

– Test order for unit and integration testing

– Change impact and version comparison

• Computation of various OO metrics• Useful for

– program comprehension and assessment

– documentation

– design and code review

– test scheduling and effort estimation

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An Object Relation Diagram

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• Generation of a cost-effective schedule – for implementing the classes (required code skeleton)

– for changing the classes

– for code review of the classes

– for testing the classes

– it effectively reduces time, effort and costs to accomplish above tasks

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Generation of Cost-Effective Test Order

Classes with test order 1:0 should be tested before classes with test order 2:0 to reduce the test effort.

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Test Stubs Required for Randomly Selected Test Sequences

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Saving from Test Order

• Average one person-hour is required to construct a test stub.

• For the InterViews library, 191.88 person-hours, or close to 5 person-weeks are required.

• Using test order, only one test stub is needed, the saving in effort and costs are tremendous even for this small program.

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Generation of Test Schedule

Critical path

Testing of classes on the critical path must be completed on time to ensure that the test process will be completed on time.

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• Computation of various OO metrics– Fan-in and fan out

– Depth of inheritance tree

– Number of lines of code

– Length of invocation chain

– Cyclomatic complexity

– Number of children, etc.

• Useful for assessing program quality and spot potential problem areas

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Various OO Metrics

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• Change impact analysis and visualization– Compare change alternatives

• Version comparison and visualization– Compare two versions/releases to identify changes and

their impact

– Visualizing the two versions/releases to facilitate code review and inspection to ensure that changes are made properly

– Useful for maintenance, release review and regression testing to reduce time, effort and costs

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Change and Impact Analysis

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Block Branch Diagram (BBD)

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Block Branch Diagram (BBD)

for test input preparation

for test case preparation

for test stub preparation

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An Overly Complex Method Is Difficulty to Comprehend and Test

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Block Branch Diagram

• Useful for white-box testing (basis path, data flow)

• Useful for state transition construction

• Useful for black-box testing

– Boundary value analysis

– Functional testing

• Initialize parameters

• Initialize input values

• Identify and construct test stubs

• Analysis of test results (changed variables)

• Used for sequence diagram reverse engineering

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Object State Diagram

• Hierarchical, concurrent, communicating state machines

• Generated from C++/Java source code using a reverse engineering approach

• Represents the dynamic state dependent behavior of objects

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allowVend: unsigned

0,0

0,0 1,M

1,M

CoinBox()

CoinBox()

Reset()

Reset() Vend()

AddQtr()

[curQtrs > 0]AddQtr()

AddQtr()

ReturnQtrs()[allowVend !=0] Vend()

S0 S1

S0 S1

curQtrs: unsigned

An Object State Diagram for an incorrect coin box class

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(S0, S0)

(S0, S0)

(S0, S0)

(S0, S0)

(S1, S1)

(S1, S1)

(S0, S1)

(S1, S1)

(S1, S0)

Reset(), ReturnQtr()

Reset(), ReturnQtr()

ReturnQtr()AddQtr()

AddQtr()

AddQtr()

Reset()

(S0, S0) (S1, S0)

ReturnQtr()Reset()AddQtr()Vend()

Vend()

Test tree showing the execution sequences of a COSD

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off, off, off

heat,off,off cool,off,off

off, off, off

SS, FR, AR

SS.heat SS.cool

heat, on, off off, off, off

off, on, off

off, off, offcool, on, offheat, on, off

off, on, off cool, on, on

SS.offFR.turnOn SS.off

SS.off

SS.heat

SS.cool

FR.turnOff

SS.off AR.turnOnSS: Season SwitchFR: Furnace RelayAR: A/C Relay

Test tree showing a flaw in a thermostat system.

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Sequence Diagram

• A sequence diagram describes the object interaction through time ordered message passing.

• Elements and their Notations– Objects

• Placed at top of the diagram across the horizontal axis

– Lifelines • Dotted lines extending down the vertical axis

– Messages and Stimulus• Horizontal solid labeled arrow.

– Focus of Control• Tall thin rectangle along the vertical axis.

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Sequence Diagram Example

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Sequence Diagram Showing a Use Case

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Usefulness of Sequence Diagram

• Understanding how use cases are implemented• Automatic generation of test cases and test data to

test the implementation• Facilitating design and code review• Check if some behavioral design patterns are

propertly implemented

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Some Application Data

• OOTWorks can process millions of lines of source code and thousands of classes

• Parsing of a 50,000 line C++ files finishes in 20 seconds

• Platform independent (Windows, Linux, Unix,Soloaris, Mac, etc.)

• Display and print very large ORD diagrams• Has been applied to real world applications with

satisfactory results

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Some Example Applications

– Identification of isolated classes

– Identification of possibly poorly designed OO software• no use of inheritance and/or aggregation

• only one parent class, all the other classes are direct children of the parent class

• classes with several thousand lines of code

• classes with very high fan-in and/or fan-out metrics

• high cyclomatic complexity

• classes having excessive number of methods may indicate poor cohesion (or too much responsibilities)

• etc.

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ORD

BBD

selected class &method

Functional Tests

Generation

Structural Tests

Generation

TestsTests

Execution

Result Analysis

Tester

using variablesused and changed

using basis paths &symbolic execution

interactivetesting

batchtesting

Possible Test Process

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ORD

OSD

selected classes

Method Sequence Tests Generation

Fault Analysis

TestsTests

Execution

Result Analysis

Tester

analysis results

Possible Test Process

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Developer

Tester

SQA

Project Manager

• time, effort and cost control• productivity and quality improvement• test scheduling

• program understanding• documentation• verification• change impact analysis• metrics

• test order• program understanding• test cases and test data preparation• regression test• metrics

Maintenance

• version comparison• change impact analysis• regression test

• verification• design and code review• metrics• documentation

Summary

Documents

Testing Object-Oriented Software A Presentation at a DFW ASEE Meeting Dr. David C. Kung