An introductory lecture to model-based testing.

1. Università degli Studi dell’Aquila
L22. Model-based Testing (Principles)
Henry Muccini
DISIM, University of L’Aquila
www.henrymuccini.com, henry.muccini@univaq.it

2. Copyright Notice
The material in these slides may be freely reproduced
and distributed, partially or totally, as far as an explicit
reference or acknowledge to the material author is
preserved.
Henry Muccini

4. Agenda
Modeling
MBT:
→Why?
→Modelsfor MBT
→UML-based Testing
─ Testing activities

5. AGENDA
Modeling
Model-based testing
Why?
Models for MBT
UML-based Testing

6. Modeling: there is not just programming
What is a model:
→A model is a simplification of the reality
→The reality is abstracted, since it is too complex
Why modeling
→Models are built for a better understanding of the
system under development
Everything is a model ?!?

7. Non-software Models …

8. Specification: What

9. Software Models

10. Other Software Models (Web models)

11. … other software models…

12. … and many others…
Pilot Pilot CoPilot CoPilot
Multifunction Multifunction Multifunction Multifunction
Display1 Display2 Display1 Display2
Display Display Display Display
Processor Processor Processor Processor
High speed network
High speed network
Mission Mission Mission
Processor Processor Processor
1553 bus
1553 bus
Auto-Pilot GPS Nav Radio

13. Model Driven Development (MDD)
Models are becoming first core assets in
Software Engineering/Architecting:
→models are primary artifacts retained as first class
entities that can be analyzed and manipulated by
means of automated tools
→the focus moves from writing and sharing
documents to writing and sharing models.

14. From Document Driven to Model Driven

15. Models in MDD
Models in MDD can be used for:
→Documenting design decisions
→Guiding the coding phase
→For analyzing and validating design choices
─ by complementing traditional code-level
analysis techniques

16. Why modeling? For Documenting and Analysis

17. What is MBT?
It consists in:
→ExtractingTest Cases from the Model
→Run the test case over the system implementation
Purpose:
→Tovalidate the implementation conformance to the
model
─ The model itself is the oracle, i.e., it represents the
expected behavior

18. Model-based Testing
A model based testing approach
accepts two main inputs
→a model of the software under test,
→a set of test generation directives which guide the test cases
selection
and outputs a test specification
→which includes a set of stimuli the tester should introduce in
the system together with expected responses

19. Modeling for testing
Essentially, we need (at least) a behavioral model of
the software system:
→Labelled Transition System
→StateCharts
→UML State of Sequence Diagrams
→IOLTS
→Finite State Automata
→…

20. The base-line technique for designing test cases
→Timely
─ Often useful in refining specifications and assessing testability
before code is written
→Effective
─ finds some classes of fault (e.g., missing logic) that can elude
other approaches
→Widely applicable
─ to any description of program behavior serving as spec
─ at any level of granularity from module to system testing.
→Economical
─ typically less expensive to design and execute than structural
(code-based) test cases
(C) 2007 MAURO PEZZÈ & MICHAL YOUNG

21. Program code is not necessary
→Only a description of intended behavior is needed
→Even incomplete and informal specifications can be used
─ Although precise, complete specifications lead to better test suites
Early functional test design has side benefits
→Often reveals ambiguities and inconsistency in spec
→Useful for assessing testability
─ And improving test schedule and budget by improving spec
→Useful explanation of specification
─ or in the extreme case (as in XP), test cases are the spec
(C) 2007 MAURO PEZZÈ & MICHAL YOUNG

22. Different testing strategies (functional, structural,
fault-based, model-based) are most effective for
different classes of faults
Functional testing is best for missing logic faults
→A common problem: Some program logic was simply
forgotten
→Structural (code-based) testing will never focus on code that
isn’t there!
(C) 2007 MAURO PEZZÈ & MICHAL YOUNG

23. Modeling for testing
Such a model can be produced:
1. Through a formal specification language
─ Typically referred as formal testing
2. Through a diagrammatic (visual) notation
─ Typically referred as UML-based Testing

24. 1. MBT based on Formal Specifications
Since the 80’s, many specification-based testing
approaches have been proposed, based on formal
languages such as
→Z, VDM, CSP, CCS, LOTOS, SDL, and Petri Nets.
More recently:
→Based on dynamic behavior:
─ FSM-based (Bochmann&Petrenko, Lee&Yannakis, …)
─ LTS-based (Brinksma&Tretmans, Jard&Jeron …)
→Focussing on static aspects,
─ ADT theory (Bernot&Gaudel…)
─ Z-based (Hierons…)

25. Formal Specification-based Testing
TorX (Côte de Resyste)
→ on-the-fly test generation and execution
→ random
→ LOTOS and Promela
TGV (IRISA - Rennes)
→derives tests in TTCN from LOTOS or SDL
→ uses test purposes
TVEDA (CNET - France Telecom)
→ derives TTCN tests from SDL specification

26. 2. MBT based on the UML
UML State-machine based testing:
→which might require the translation of the UML
diagrams into an intermediate formal description
Scenario-based testing:
→based on the use of opportunely annotated UML Sequence Diagram
State-based and Scenario-based:
combine the use of interaction diagrams and state diagram,
possibly annotated with further (formal) information (e.g. OCL)

27. Model-based Testing: the overall idea
From Leila Naslavsky Advancement report

28. AsmL
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TESTO
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UMLAU
UT
Model-based Testing Approaches
UMLTe
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AGEDI
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TOTEM
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TF
COW-SU
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SCENTO
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UCSC-Sy
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29. Main Testing Activities
Test Selection/Generation:
→it consists in selecting a suitable and finite set of test cases
from the possibly infinite set;
Test Execution and Evaluation:
→it consists in executing the code accordingly to the selected
test cases and comparing real and expected results;

30. Test Selection
A test case, in MBT, is typically a possible
“scenario”
→In scenario-based testing:
─ A scenario itself is an abstract test case
→In state-based testing
─ Execution flows are extraced from the state machine
and represent a test case
─ MB coverage criteria are applied on this model

31. Test Case Selection
Abstract Test case = path over the LTS/FSM,
corresponding to sequences of events
─ They are not “concrete” test cases, but abstract
(depending on the specification)
→Concrete Test cases = mapping asbtract test cases
into execution statements to be launched

32. Test Case Selection
Model of the
Test system
directives
inSD 1
1
C1 C2
m9
m1
Test
specification
outSD1
2 C1 C2 C3
m9
m3
m8
m1

33. Test Case Selection

34. Test Execution
It consists in running the test cases on the system
implementation
→So to compare the real execution with the expected behavior

35. MBT practical concerns
Traceability, i.e. relating the abstract values of the
specification to the concrete values of the
implementation.
Execution, i.e. forcing the Implementation Under Test
(IUT) to execute the specific sequence of events that
has been selected.

36. Testing and Industry
In order to be suitable for industrial needs a testing
approach has to emphasize the following qualities:
→Usability
─ Not ad-hoc models
→Timeliness
─ Soon and even incomplete
Opposed to
→Tool support accuracy
Goal of a suitable testing approach should be
“to improve the test results accuracy without sensibly
raising the testing effort”

37. MBT Tools
There are some automated tools for MBT:
→Telelogic Tau and Tau Tester
→Leirios Test Designer
→Conformiq Qtronic
→Rhapsody Test Conductor and Automatic Test Generation
→AGEDIS

38. MBT in industry: challenges and issues
As remarked by Alan Hartman in his 2006 speech at ISSTA:
→“Only 1% of industry uses it”
Why?

39. Why?
The main reasons I foresee:
→Model2Code (and viceversa) traceability problems
→modeling is not yet so widely recognized as part of
the development process.
─ Legacy systems
→because of tool/service problems
→cost/effectiveness is still under exploration

40. Conformiq: Two models are required in
Input
•SutModel.Java (in QML)
•SutModel.xmi (Graphical Notation)

41. QML
Just like Java, QML consists of variables and
expressions, all strictly typed and known before the
compilation.
The types are divided into the same three groups that
Java has: primitives, references and values

42. QML
QML extends Java with:
Records
Ports
System block
State machines

43. SutModel Graphical

44. SutModel Graphical

45. Coverage
Figure 5 – The Coverage Editor window