XML-based Testing of Web Software Services Joint research with Wuxhi Xu, Juan Luo and Suet Chun Lee Jeff Offutt Software Engineering George Mason University

XML-based Testing of Web Software Services

Joint research withJoint research with Wuxhi Xu, Juan Luo and Suet Chun Lee Wuxhi Xu, Juan Luo and Suet Chun Lee

Jeff OffuttJeff OffuttSoftware EngineeringSoftware Engineering

George Mason UniversityGeorge Mason University

Fairfax, VA USAFairfax, VA USA

www.cs.gmu.edu/~offutt/www.cs.gmu.edu/~offutt/

[email protected]@gmu.edu

Need for Reliable Web Apps• Expedia sells more than $35 million in tickets weekly

– Based on 2000 data

• In Dec 2006, amazon.com’s BOGO offer turned into a double discount

• Huge losses on web application failures– Financial services : $6.5 million per hour

– Credit card sales applications : $2.4 million per hour

– Media companies : $150,000 per hour

• Most faults introduced during maintenance• Most security vulnerabilities are due to software faults

STEP 2008 © Jeff Offutt 2

Research in Software Testing


Growth fueled by need for better softwareGrowth fueled by need for better software

Research LaboratoriesResearch LaboratoriesMicrosoftMicrosoft

GoogleGoogleSiemensSiemens

…… Conferences & WorkshopsConferences & Workshops

ICSTICSTISSREISSRE

STEP workshopSTEP workshopMBTMBTASTAST……

University GroupsUniversity GroupsFITFIT

GMUGMUUNLUNL

……

University / Industry University / Industry PartnershipsPartnerships

FedEx / U MemphisFedEx / U Memphis

UsefulUseful ways to build better software ways to build better software

Travel Information Flow


dates dates airportsairports

checkin

schedule

seats

reservation

checkin

rooms phones schedul

es

Airline

flights

nameflights

Organizers

Spouse

Hotel

Agent

Airport

Colleagues

contact schedul

e

room

receipt

meeting rooms

confirm

gate

checkoutTraveler

Travel Information Needed


dates dates airportsairports

checkin

schedule

seats

reservation

checkin

rooms phones schedul

es

Airline

flights

nameflights

Organizers

Spouse

Hotel

Agent

Airport

Colleagues

contact schedul

e

room

receipt

meeting rooms

confirm

gate

checkout

Information NeededConference scheduleHotel address & phone numberFlight numbers and timesGate numbersSeat numbersHotel confirmation numberHotel room numberMeeting rooms and timesLocal contact information for colleagues

…

And after returning home …And after returning home …all this information is immediately discarded !all this information is immediately discarded !

Current Method• Most of us accumulate this information from

– Email– Websites– Phone conversations– Personal conversations– Pieces of paper

• And then try to organize and track it– In our heads– Random scraps of paper– Laboriously hand-entering data into hand-held devices


This is very 20This is very 20thth century analog …century analog …

21st Century Method

• Data are sent to a hand-held device wirelessly– Hand-held device automatically organizes data into

meaningful information

• Information is presented to traveler when needed


Data are generated and sent Data are generated and sent through software in athrough software in a

service oriented architectureservice oriented architectureservice oriented architectureservice oriented architecture

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Web Services• A Web Service is a program that offers services over

the Internet to other software programs– Internet-based– Uses SOAP and XML– Peer-to-peer communication via message passing

• Web service components can integrate dynamically, by finding other services during execution

• Web services transmit data formatted in XML

STEP 2008

What does a service oriented architecture look like ?What does a service oriented architecture look like ?

© Jeff Offutt 9

Web Service Architecture

Web ServicesWeb Services

serverserver

Laptop

PDA

Work-station

Cell phone

Web AppsWeb Apps

internet

servers

clients

Client-serverClient-server

server

clients

STEP 2008

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Web Service Technologies

WSDL Specification

Specification

ComponentsLegacy Systems

Wrapped

Specification

UDDI Registry

ServicesWrapped

ApplicationsSOAP / XML Points to URL

SOAP / XML

Publish Publish

Find Find

Bind Bind

STEP 2008

messages transmitted in XMLmessages transmitted in XML

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Why XML ?• Software components that pass data must agree on format,

types, and organization• Web services have unique requirements :

– Very loose coupling and dynamic integration

1970s style

P1 P2

FileFile storage

Un-documented format

Data saved in binary mode

Source not available

1980s style

P1 P2

File

WM

File storage

Un-documented format

Data saved as plain text

Access through wrapper module

Data hard to validate

STEP 2008

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XML

• Data is passed directly between components• XML allows for self-documenting data

2000s style

Schemas

P1P2

Parser

XMLFile

P3

• P1, P2 and P3 can see the format, contents, and structure of the data

• Data sharing is independent of type• Format is easy to understand• Grammars are defined in schemas

STEP 2008

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XML for Flight Example

• XML messages are defined by grammars (schemas)

• Schemas can define many kinds of types• Schemas include “facets,” which refine the grammar

<flights> <flight> <airline>USAir 2608</airline> <origin>IAD</origin>

<destination>CLT</destination>

<leavetime>10:50:00</leavetime>

<arrivetime>12:11:00</arrivetime>

<date>2008-05-04</date> </flight></flights>

STEP 2008

schemas define input spaces for software componentsschemas define input spaces for software components

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Input Space Grammars

• The input space can be described in many ways

– User manuals

– Unix man pages

– Method signature / Collection of method preconditions

– A language

• Most input spaces can be described as grammars• Grammars are usually not provided, but creating them is a

valuable service by the tester– Errors will often be found simply by creating the grammar

Input SpaceInput Space

The set of allowable inputs to softwareThe set of allowable inputs to software

STEP 2008

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Using Input Grammars• Software should reject or handle invalid data• Programs often do this incorrectly• Some programs (rashly) assume all input data is correct• Even if it works today …

– What about after the program goes through some maintenance changes ?

– What about if the component is reused in a new program ?

• Consequences can be severe …– The database can be corrupted

– Users are not satisfied

– Most security vulnerabilities are due to unhandled exceptions … from invalid data

STEP 2008

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Validating Inputs

• Before starting to process inputs, wisely written programs check that the inputs are valid

• How should a program recognize invalid inputs ?• What should a program do with invalid inputs ?• If the input space is described as a grammar, a parser can

check for validity automatically– This is very rare

– It is easy to write input checkers – but also easy to make mistakes

Input ValidationInput Validation

Deciding if input values can be processed by the softwareDeciding if input values can be processed by the software

STEP 2008

Representing Input Domains


Desired inputs (goalgoal domain)

Described inputs (specifiedspecified domain)

Accepted inputs (implementedimplemented

domain)

Representing Input Domains• Goal domains are often irregular• Goal domain for credit cards†

– First digit is the Major Industry Identifier

– First 6 digits and length specify the issuer

– Final digit is a “check digit”

– Other digits identify a specific account

• Common specified domain– First digit is in { 3, 4, 5, 6 } (travel and banking)

– Length is between 13 and 16

• Common implemented domain– All digits are numeric


† More details are on : http://www.merriampark.com/anatomycc.htm

Representing Input Domains


goalgoal domain

specifiedspecified domain

implementedimplemented domain

This region is a rich source of software errors …This region is a rich source of software errors …

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Testing Web Services

• This form of testing allows us to focus on interactions among the components

• A formal model of the XML grammar is used• The grammar is used to create valid as well as

invalid tests• The grammar is mutated• The mutated grammar is used to generate new

XML messages• The XML messages are used as test cases

STEP 2008

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XML Data Model Example<xsd:element name = “flights”> <xsd:complexType> <xsd:sequence> <xsd:element name = “flight” maxOccurs = “unbounded”> <xsd:complexType> <xsd:sequence> <xsd:element name = “airline” type = “xsd:string”/> <xsd:element name = “origin” type = “airportType”/> <xsd:element name = “destination” type = “airportType”/> <xsd:element name = “leavetime” type = “xsd:time”/> <xsd:element name = “arrivetime” type = “xsd:time”/> <xsd:element name = “date” type = “xsd:date”/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType></xsd:element>

<xs:simpleType name = “airportType”> <xs:restriction base = “xsd:string”> <xs:length value = “3” /> </xs:restriction></xs:simpleType>

STEP 2008

Built-in typesBuilt-in types

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XML Constraints – “Facets”

Boundary Constraints

Non-boundary Constraints

maxOccurs enumeration

minOccurs use

length fractionDigits

maxExclusive pattern

maxInclusive nillable

maxLength whiteSpace

minExclusive unique

minInclusive

minLength

totalDigitsSTEP 2008

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XML Data Model

An XML schema can be modeled as a tree

T T = (= (N, D, X, E, nN, D, X, E, nrr))

N is a finite set of elements and attribute nodes

D is a finite set of built-in and derived data types

X is a finite set of constraints

E is a finite set of edgesEdges are from N to ND, plus a constraint

nr is the root node

STEP 2008

Generating Tests• Valid tests

– Generate tests as XML messages by deriving strings from grammar

– Take every production at least once– Take choices … “maxOccurs = “unbounded” means use

0, 1 and more than 1

• Invalid tests– Mutate the grammar in structured ways– Create XML messages that are “almost” valid– This explores the gray space on the previous slide


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Mutation Operators

Every nonterminal symbol in a production is replaced by other nonterminal symbols.

1. Nonterminal Replacement

Every terminal symbol in a production is replaced by other terminal symbols.

2. Terminal Replacement

Every terminal and nonterminal symbol in a production is deleted.

3. Terminal and Nonterminal Deletion

Every terminal and nonterminal symbol in a production is duplicated.

4. Terminal and Nonterminal Duplication

STEP 2008

These operators are designed to mimic common These operators are designed to mimic common XML errorsXML errors

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Test Case Generation

• A test case is an XML message

• Tests are generated directly from mutated schemas

• Constraints are “violated” systematically– Values beyond the boundary values

• “maxLength=5” “abcdef”

– Values outside the non-boundary constraints• “fractionDigits=2” “456 . 324”

• Multiple XML messages from the same schema

• Messages are invalid, so a valid response is an error– False positives : Messages that are accidentally valid

STEP 2008

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Test Case Generation – ExamplesOriginal Schema (Partial)

<xs:simpleType name = “priceType”> <xs:restriction base = “xs:decimal”> <xs:fractionDigits value = “2” /> <xs:maxInclusive value = “1000.00” /> </xs:restriction></xs:simpleType>

Mutants : value = “3”

value = “1”

Mutants : value = “100”

value = “2000”

XML from Original Schema<books> <book> <ISBN>0-201-74095-8</ISBN> <price>37.95</price> <year>2002</year> </book></book>

Mutant XML 1<books> <book> <ISBN>0-201-74095-8</ISBN> <price>37.95 </price> <year>2002</year> </book></book>

505

Mutant XML 2<books> <book> <ISBN>0-201-74095-8</ISBN> <price>37.95</price> <year>2002</year> </book></book>

5


101.00


1001.00

STEP 2008

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Case Study 1• Small web service created at GMU

– Three components : Mars robot, space station, ground control– Ground control is a three-tier web application

• Correct behavior is to have abnormal responses– Receiver cannot process the data, responds with a fault– Receiver has a runtime exception

• Three types of mutants– Deletion, Insertion, Constraint Violation

D I CV Original Total

XML Schemas 23 25 11 4 63

XML Messages 64 103 53 12 232

Abnormal Response 64 103 11 0 178

Normal Response 0 0 42 12 5442

Only CV tests got Only CV tests got normal responsesnormal responses

STEP 2008

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Case Study 2

• From Web Services Interoperability Organization– Supply chain management

– Seven XML schemas

– Three were requests and used for invalid tests

Mutated Schemas

Schema D I CV

Retailer 14 83 9

Warehouse 6 22 3

Manufacturer 8 32 3

XML Messages

D I CV

129 710 90

15 48 6

14 48 3

• Fifteen faults inserted into the program• Seven faults found – all by CV tests

STEP 2008

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Analysis of Faults

8 faults not found

• 5 faults : Affected back-end log file– Observability … log file was not seen

• 1 fault : Depends on inputs from the database– Controllability … tests depend on XML, not DB

• 2 faults : Required specific values that were not used

• All Deletion and Insertion tests were detected by program

STEP 2008

Discussion

• Deleting and inserting parts of the grammar have little or no value

• Observability and controllability are major problems with web services– This is well-documented with web applications

• The constraints are much more useful for generating tests than deleting and inserting XML elements


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Extensions Needed• Improve invalid test generation

– Focus on constraint-based tests from tests– Expand mutation of constraint

• Automatic test generation– Based on input space partitioning (category

partitioning)

• General problems– Dealing with observability– Dealing with controllability

STEP 2008

Travel Info Flow – Web Services


Organizers

email

Airline

Agentdesired travel info

web app

web servic

etravel

info

web servic

esTraveler

Traveler

Use web services instead of email to plan trip

Airport

wireless web

service connecti

on

checkin gate info

Hotel

wireless web

service connecti

on

checkin checkout room

key

Connect wirelessly to web services during journey

initial schedule

Travel Info Flow – Web Services• Traveler will send requirements to travel agent and hotel• Information will be sent to traveler’s web service, which

will store it on the traveler’s hand-held device• Traveler will check-in at the airport by beaming data from

hand-held– Airport will send gate information and a map to the hand-held

• Traveler will check in and out of hotel by beaming data from hand-held– Hotel will send hotel room, map, and electronic key to hand-held

• Conference organizers will send meeting organization details to room computer, which will sync with hand-held

• Room computer will send contact details to spouseSTEP 2008 © Jeff Offutt 34

Trusting Web Services

• Reliable

• Secure

• Dependable

• Usable


For widespread adoption, users must For widespread adoption, users must be confident web services arebe confident web services are

Conclusions• This mode of operation will be more convenient and

efficient– Reduces the need to laboriously hand-translate

information from one device or format to another

• All of the technologies to support these interactions are available

• We are missing some engineering– Reliable web services– Secure data transmission– Usable interfaces


Testing addresses Testing addresses some, but not all some, but not all these issuesthese issues

© Jeff Offutt 37

Contact

Jeff OffuttJeff Offutt

[email protected]@gmu.edu

http://cs.gmu.edu/~offutt/http://cs.gmu.edu/~offutt/

STEP 2008

Documents

XML-based Testing of Web Software Services Joint research with Wuxhi Xu, Juan Luo and Suet Chun Lee Jeff Offutt Software Engineering George Mason University