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Software Testing: A Craftsman’s Approach, 4th Edition Chapter 12 Model-Based Testing

Chapter 12

Model-Based Testing


Overview of Model Based Testing (MBT)

•  An iterative process •  Start by modeling the

System Under Test (SUT) •  Derive test cases from

the model •  Execute test cases

–  Record coverage –  Trace to model

•  Modify model as needed •  Repeat steps

testing

modeling


Modeling the System Under Test (SUT)

•  Models were developed to meet the needs of the systems being analyzed –  issues inherent in the system must be expressed –  Petersen’s Lattice presents a nice selection (but

dated) of behavioral models •  The hard part—picking the “right” model,

–  not too powerful –  not too weak –  “necessary and sufficient

•  We will spend some time on Peterson’s Lattice and recent updates.


ExtendedPetri Nets

Message Systems

Semaphore (P, V) Systems

VectorReplacement

Systems

VectorAdditionSystems

Petri Nets UCLA Graphs

Marked Graphs

Finite State Machines

Peterson’s Lattice of Behavioral Models

James L. Peterson, Petri Net Theory and the Modeling of Systems, Prentice Hall, Englewood Cliffs, NJ, 1981


About Peterson’s Lattice •  In mathematics, a lattice represents a “partial

ordering” in which one element is “greater than” an adjacent element.

•  In Peterson’s Lattice, the ordering relation is “more expressive than”

•  In his book, Peterson shows, for each edge in the lattice, an example that cannot be represented in the weaker system and can be represented in the stronger one.

•  But, he wrote in in 1981.


Petri Net 5, 6, 7

SemaphoreSystem

3, 4

MarkedGraph

1

Finite StateMachine

2

Expressive Capabilities in Peterson’s Lattice

•  Numbers correspond to regions in the diagram –  1 data flow –  2 control flow –  3 conflict –  4 mutual exclusion –  5 fair scheduling –  6 communication –  7 synchronization


Updating Peterson’s Lattice •  Three of the four equivalent models (vector

replacement systems, vector addition systems, and UCLA Graphs) are seldom used.

•  Petri nets are usually extended. •  Message systems and semaphore systems are

generally language based. •  BUT Peterson’s book predates David Harel’s elegant

StateChart notation.


ExtendedPetri Nets

Message Systems

Semaphore (P, V) Systems

VectorReplacement

Systems

VectorAdditionSystems

Petri Nets UCLA Graphs

Marked Graphs


StateCharts

Where do StateCharts Belong?


About StateCharts

•  (see Chapter 4!) •  Harel’s main goal was to combine the expressive

powers of Directed Graphs and Venn Diagrams. •  StateCharts have

–  a sense of hierarchy –  ability to describe concurrent devices –  memory –  history –  and a very expressive language on transitions

•  Clearly more expressive than (most) extensions to Petri Nets.


Extensions to Peterson’s Lattice

•  Event-Driven Petri Nets –  Jorgensen, 1985

“The use of mm-paths in constructive software development”, Dissertation, Arizona State University

–  chapter 4 in this book •  StateCharts

–  David Harel, 1988 •  UML StateCharts (after 1998) •  Swim Lane Petri Nets

–  DeVries 2013 •  (see text for full references)


Event-DrivenPetri Nets

UML StateCharts

Petri Nets

Swim Lane Event-Driven

Petri Nets

Swim Lane Petri Nets

?

Extensions to Peterson’s Lattice


Sources of Behavioral Issues Behavioral Issue Source of Issue

sequence

Structured Programming selection

repetition

enable

Extended Systems Modeling Language

disable

trigger

activate

suspend

resume

pause


Sources of Behavioral Issues (continued) Behavioral Issue Source of Issue

Conflict

Task Management

priority

mutual exclusion

concurrent execution

deadlock

context sensitive input events

Events multiple context output events

asynchronous events

event quiescence


Expressive Capabilities of Selected Behavioral Models

Behavioral Issue

Decision Tables


Petri Nets

Event- Driven Petri Nets

Statecharts

sequence no yes yes yes yes selection yes yes yes yes yes repetition yes yes yes yes yes enable no no yes yes yes disable no no yes yes yes trigger no no yes yes yes activate no no yes yes yes suspend no no yes yes yes resume no no yes yes yes pause no no yes yes yes


Expressive Capabilities of Selected Behavioral Models (continued)

Behavioral Issue Decision Tables

Finite State

Machines

Petri Nets

Event-Driven Petri Nets

State charts

conflict no no yes yes yes priority no no yes yes yes mutual exclusion yes no yes yes yes concurrent execution no no yes yes yes deadlock no no yes yes yes context sensitive input events yes yes no yes yes multiple context output events yes yes no yes yes asynchronous events no no no yes yes event quiescence no no no yes yes


“Procedure” for Model-Based Testing

•  Understand application to be modeled •  Identify behavioral issues in the application •  Use previous slides to select “appropriate” model

–  this may depend on staff talent –  or existing development tools –  or other immutable requirements

•  Model the application •  Use an engine to “execute” the model, thereby

identifying –  interesting scenarios –  automatically generated test case (skeletons)


Example for Model-Based Testing

•  Based on the Simple ATM system (SATM) •  One thread: Correct PIN on first try •  Finite State Machines decomposed into a hierarchy

–  Uppermost Level •  PIN Entry state

– PIN try states •  Derived Port Event Sequence for Correct PIN on

first try •  Expanded Essential Use Case for Correct PIN on

first try


Uppermost Level SATM Finite State Machine S1: Idle

(Welcome Screen)

S2: PIN Entry

S3: Transactionprocessing

S4: AnotherTransaction?

S5: Close ATMSession

Invalid Card/screen 4

Valid Card/screen 2

Valid PIN/screens 5 then 6Invalid PIN/screen 3

3rd PIN attempt failedscreen 1

Withdrawals

BalanceInquiry Deposits

No/screen 14

Yes

Timeout screen 15


PIN Entry Finite State Machine

Valid PINscreen 5

Invalid PINscreen 3

S1: Idle

S2: 1st PIN try

S2: 1st PIN try

S2: PIN Entry

S4: 3rd PIN try

S3: TransactionChoice

Valid PINscreen 5

Valid PINscreen 5

Invalid PINscreen 3

Invalid PINscreen 1


PIN Try Finite State Machine

S3: Transaction Choice

1st digit echo ‘---*’

S1: Idle

S2.n: nth PIN try

S2.n.1: 1 digitreceived

S2.n.2: 2digitsreceived

S2.n.3: 3 digitsreceived

S2.n.4: 4digitsreceived

2nd digit echo ‘--**’

3rd digit echo ‘-***’

4th digit echo ‘****’

Enter key, Valid PINscreen 5

Enter key, Invalid PIN

S2.n.0: 0 digitsreceived

S2.n.6: Retrydecision

Cancel

Cancel

Cancel

Cancel

Cancel

Try n < 3screen 3

Try n = 3screen 1


Derived Port Event Sequence for Correct PIN on first try

Port Input Event Port Output Event

Screen 2 displayed with ‘- - - -’

1st digit

Screen 2 displayed with ‘- - - *’

2nd digit

Screen 2 displayed with ‘- - * *’

3rd digit

Screen 2 displayed with ‘- * * *‘

4th digit

Screen 2 displayed with ‘* * * *’

Enter touched

Screen 5 displayed


Expanded Essential Use Case for Correct PIN on first try

Use Case Name Correct PIN entry on first try Use Case ID EEUC-1 Description A customer enters the Pin number

correctly on the first attempt. Pre-Conditions 1. The expected PIN is known

2. Screen 2 is displayed Event Sequence

Input events Output events 1. Screen 2 shows '- - - - ' 2. Customer touches 1st digit 3. Screen 2 shows '- - - * ' 4. Customer touches 2nd digit 5. Screen 2 shows '- - * * ' 6. Customer touches 3rd digit 7. Screen 2 shows '- * * * ' 8. Customer touches 4th digit 9. Screen 2 shows '* * * * ' 10. Customer touches Enter 11. Screen 5 is displayed Post conditions Select Transaction screen is active

Software Testing: A Craftsman’s Approach, 4th Edition Chapter 12 Model-Based Testing Software Testing: A Craftsman’s Approach, 3rd Edition Model-Based Testing

Commercial Tools for Model-Based Testing (from Practical Model-Based Testing, by Mark Utting and Bruno Legeard)

Tool Name Company Web Link Conformiq Test Generator

Conformiq www. conformiq.com

LEIROS LTG/B and LTG/UML

LEIROS Technologies

www.leiros.com

Reactis Reactive Systems

www.reactive-systems.com

StateMate (also Rhapsody)

IBM http://pic.dhe.ibm.com/infocenter/rhaphlp/v7r5/index.jsp?topic=%2Fcom.ibm.rhapsody.designing.doc%2Ftopics%2Frhp_c_dm_rning_anm_models.html

TAU Tester IBM http://www-01.ibm.com/software/rational/

ZigmaTESTTools ATS www.atssoft.copm

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