Model Based Testing

Texas A&M University

Department of Computer Science

Sameh S. Sharkawi

Outline Introduction

What is MBT Motivation behind MBT

How MBT Works Benefits of MBT Problems of MBT Current State of MBT in Industry Software Tools for MBT Conclusion References

Introduction (What is MBT) Definition

“Model-based testing refers to software testing where test cases are derived in whole or in part from a model that describes some (usually functional) aspects of the system under test (SUT) .” *

* Wikipedia Definition of Model Based Testing.

Introduction (What is MBT Contd.) MBT is an approach in which you define the

behavior of a system in terms of actions that change the state of the system.

Such a model of the system results in a well-defined Finite State Machine (FSM) which helps us to understand and predict the system’s behavior

Introduction (Motivation behind MBT) Testing is expensive

30-50% of development costs Poor testing is VERY expensive

Down time Maintenance costs Rework Law suits

Model Based Testing promises Increased effectiveness of testing Similar or decreased costs Reuse of design artifacts

Introduction (Motivation behind MBT Downtime Costs) Brokerage operations $6,450,000 Credit card authorization $2,600,000 Ebay (1 outage 22 hours) $225,000 Amazon.com $180,000 Package shipping services $150,000 Home shopping channel $113,000 Catalog sales center $90,000 Airline reservation center $89,000 Cellular service activation $41,000 On-line network fees $25,000 ATM service fees $14,000

How MBT Works

How MBT Works? The model is usually an

abstract, partial presentation of the system under test's desired behavior.

The test cases derived from this model are functional tests on the same level of abstraction as the model.

These test cases are collectively known as the abstract test suite

How MBT Works? Contd. The abstract test suite cannot

be directly executed against the system under test because it is on the wrong level of abstraction.

Therefore an executable test suite must be derived from the abstract test suite that can communicate with the system under test.

This is done by mapping the abstract test cases to concrete test cases suitable for execution.

How MBT Works? Contd. Deriving Test Cases Algorithmically

Test Case Generation by Theorem Proving Test Case Generation by Constraint Logic

Programming Test Case Generation by Model Checking Test Case Generation by Symbolic Execution

How MBT Works? Contd.

Spec Explorer (UW-MSR Summer Institute '04)

Model

Implementation

Test OracleTest Cases

Run Providesactual results for

Provides expected results forGenerates

PassFail

Benefits of MBT

Benefits of MBT Starting from specification

Involves testers early in the development process Teams testers with developers Forces testability into product design

Building the test interface Finds design and specification bugs - before code exists The model is the test plan - and is easily maintained Automated test suite generation Coverage is guaranteed - increases testing thoroughness Zero test suite maintenance costs

Automated test suite execution Finds code and interface bugs Includes a framework for the testing of distributed

applications Reduces test execution costs

Benefits of MBT Contd. These benefits can be summarized as:

Machine Time

Benefits of MBT Contd. Machines

A typical test engineer Earns €41 500 ($50 000 USD) per year Works 40 to 50 hours per week

A typical test machine Costs €250 ($300 USD) per year to buy and operate Can work 100 hours per week

Benefits of MBT Contd.

react.cs.uni-sb.de/mbt2006/talks/mbt4masses.pdf

Problems of MBT

Problems of MBT

Problems of MBT Contd.

Problems of MBT Contd.

Problems of MBT Contd.

Problems of MBT Contd.

Process shift Up front investment in test

Personnel shift Higher education and sophistication

Spec Explorer (UW-MSR Summer Institute '04)

Current State of MBT in Industry

Current State of MBT in Industry IBM Research

Most projects were done by PhD Holders Very Little was successful (Just in the Lab, never

actually went into market) Too Complicated to use and analyze

Microsoft Research The Spec# programming system is a new attempt

at a more cost effective way to develop and maintain high-quality software

Current State of MBT in Industry Spec# is a computer language which

includes and extends C# Adds pre/post conditions, contracts Adds high-level data types with convenient

notations Adds logical quantifiers like FORALL and EXISTS

A Spec# model is just a program! You can run it like a C# program It can call framework code NEW You can explore it (run all of its possible

behavior) which is how we do MBT with Spec#

Spec Explorer (UW-MSR Summer Institute '04)

Current State of MBT in Industry (Spec Explorer) A model exploration and testing tool

for .NET: Authoring of models in Word Model exploration (generating FSM) FSM visualization FSM traversal and test suite generation Automatic implementation binding Online test-suite execution and offline test-suite

code generation

Spec Explorer (UW-MSR Summer Institute '04)

Current State of MBT in Industry (Spec #)

Model: Calculator (viewpoint: only starting and stopping, and switching scientific mode)

bool Running = false;bool Scientific = false;

[Action] void SetRunning(bool newRunning) requires Running != newRunning; { Running = newRunning;}

[Action] void SetScientific(bool newScientific) requires Running; requires Scientific != newScientific; { Scientific = newScientific;}

System State

Spec#: Pre-Condition

describes when action is enabled

State Update

Tells Spec Explorer

this is an action. Action

invocations do appear in tests.Spec Explorer (UW-MSR Summer Institute '04)

Software Tools for MBT

Software Tools for MBT Conformiq Test Generator is a model-based testing tool

using UML state charts that represent testing strategies Leirios Test Generator is a model-based testing tool that

generates tests automatically from deterministic system specifications

Reactis Tester is another model-based testing tool that focuses on control systems

TGV is a tool for the generation of conformance test suites for protocols

TorX is also a prototype testing tool for conformance testing of reactive software

Lurette is an automated testing tool of reactive programs written in Lustre

AsmL Test Tool can generate tests directly from an AsmL model

AutoFocus (in german) is a graphical tool for developing and modeling distributed systems with integrated testing facilities

Software Tools for MBT (AsmL) AsmL is the Abstract State Machine

Language. It is an executable specification language based on the theory of Abstract State Machines. The current version, AsmL 2 (AsmL for Microsoft .NET), is embedded into Microsoft Word and Microsoft Visual Studio.NET. It uses XML and Word for literate specifications. It is fully interoperable with other .NET languages. AsmL generates .NET assemblies which can either be executed from the command line, linked with other .NET assemblies, or packaged as COM components.

Conclusion

Conclusion Modeling is not easy

What details do you leave out? How do you check the model? There are no recipes for success

What needs to happen Easier notation Incremental approach Pilots and examples

Questions How do we guarantee that the generated

expected outputs and inputs are enough and cover all the cases?

How to make for the errors and exceptions that may occur due to running the program on different environments and different OSs?

How is automated generation of inputs and outputs work when an actual human interaction is required as part of the system testing?

Does MBT cover stress testing? Does MBT cover how user friendly the

system is or it only covers functionality?

References

References http://en.wikipedia.org/wiki/Model-based_testing http://blogs.msdn.com/nihitk/articles/144664.aspx http://research.microsoft.com/specsharp/ http://react.cs.uni-sb.de/mbt2006/talks/

mbt4masses.pdf http://react.cs.uni-sb.de/mbt2006/talks/

ModelBasedTestingSoberEvaluation.pdf http://aetgweb.argreenhouse.com/papers/1999-

icse.pdf Colin Campbell, Wolfgang Grieskamp,

Lev Nachmanson, Wolfram Schulte, Nikolai Tillmann, Margus Veanes “Spec Explorer:An Integrated Environment for Model-Based Testing.” Foundations of Software Engineering Microsoft Research, Redmond