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Software Testing: A Newcomer’s Guide
Paul AmmannSoftware Engineering Group
George Mason University
Presented at ICST April 2, 2009
Denver, ColoradoSlides Co-Produced with Jeff Offutt
Software Testing: A Newcomer’s Guide © 2009 22
Here! Test This!
Testing two decades ago
A stack of computer printouts—and no documentation
Testing a decade agoTesting Now?
A disk – and no documentationA complex conglomeration – only low level documentation
Software Testing: A Newcomer’s Guide © 2009 33
A Talk in 4 Parts1. Why do we test ?
Costs and Attitudes
2. What should we do during testing ? Test Activities Software Testing Terms Evolving Notion of Coverage Criteria
3. How do we get to this future of testing ? Beizer’s Maturity Levels
4. Background for ICST sessions
We are in the middle of a revolution in how software is tested
Research is finally meeting practice
Software Testing: A Newcomer’s Guide © 2009 44
Part 1 : Why Test?
Written test objectives are rare or useless– “The software shall be easily maintainable” – What fact is each test trying to verify?
Requirements definition teams should include testers! – Ensures testing can satisfy test objectives– Provides rationale for tests
How much testing is enough?
If you don’t know why you’re conducting a test, it won’t be very helpful
Software Testing: A Newcomer’s Guide © 2009 55
Cost of Testing
In the real-world, testing is the principle post-design activity
Restricting early testing usually increases cost
Extensive hardware-software integration requires more testing
You’re going to spend at least half of your development budget on testing, whether you want to or not
Software Testing: A Newcomer’s Guide © 2009 66
Cost of Not Testing
Not testing is even more expensive
Planning for testing after development is prohibitively expensive
Hardware developers spend huge amounts on testing …
Software test tools aren’t that expensive. Many are free!!!
Program Managers often say: “Testing is too
expensive.”
Software Testing: A Newcomer’s Guide © 2009 77
Caveat: Impact of New Tools and Techniques
They’re teaching a new way of plowing over at the Grange tonight - you going?
Naw - I already don’t plow as good as I know how...
Good Techniques and Tools are Not Enough:Practitioners Need to Adopt Them Too!
Software Testing: A Newcomer’s Guide © 2009 88
Part 2 : What ?
But … What should we do ?
1. Types of test activities2. Software testing terms3. Changing notions of testing
– test coverage criteria– criteria based on structures
Software Testing: A Newcomer’s Guide © 2009 99
Testing in the 21st Century We are going through a time of change Software Defines Behavior
– network routers– financial networks– telephone switching networks– other infrastructure
Embedded Control Applications– airplanes, air traffic control– spaceships– watches– ovens– remote controllers
Safety critical, real-time software Web apps must be highly reliable And of course … security is now all about software faults !
– PDAs– memory seats – DVD players– garage door openers– cell phones
Testing ideas have matured enough to be used in practice
Software Testing: A Newcomer’s Guide © 2009 10
Test Activities Testing can be broken up into four general types of activities
1. Test Design2. Test Automation3. Test Execution4. Test Evaluation
Each type of activity requires different skills, background knowledge, education and training
No reasonable software development organization uses the same people for requirements, design, implementation, integration and configuration control
10
Why do test organizations still use the same people for all four test activities??
This is clearly a waste of resources
1.a) Criteria-based
1.b) Human-based
Software Testing: A Newcomer’s Guide © 2009 11
1. Test Design – (a) Criteria-Based
This is the most technical job in software testing Requires knowledge of :
– Discrete math– Programming– Testing
Requires much of a traditional CS degree This is intellectually stimulating, rewarding, and challenging Test design is analogous to software architecture on the
development side Using people who are not qualified to design tests is a sure way to
get ineffective tests
11
Design test values to satisfy coverage criteria or other engineering goal
Software Testing: A Newcomer’s Guide © 2009 12
1. Test Design – (b) Human-Based
This is much harder than it may seem to developers Criteria-based approaches can be blind to special situations Requires knowledge of :
– Domain, testing, and user interfaces Requires almost no traditional CS
– A background in the domain of the software is essential– An empirical background is very helpful (biology, psychology, …)– A logic background is very helpful (law, philosophy, math, …)
This is intellectually stimulating, rewarding, and challenging– But not to typical CS majors – they want to solve problems and build
things
12
Design test values based on domain knowledge of the program and human knowledge of testing
Software Testing: A Newcomer’s Guide © 2009 13
2. Test Automation
This is slightly less technical Requires knowledge of programming
– Fairly straightforward programming – small pieces and simple algorithms Requires very little theory Very boring for test designers Programming is out of reach for many domain experts Who is responsible for determining and embedding the expected
outputs ?– Test designers may not always know the expected outputs– Test evaluators need to get involved early to help with this
13
Embed test values into executable scripts
Software Testing: A Newcomer’s Guide © 2009 14
3. Test Execution
This is easy – and trivial if the tests are well automated Requires basic computer skills
– Interns– Employees with no technical background
Asking qualified test designers to execute tests is a sure way to convince them to look for a development job
If, for example, GUI tests are not well automated, this requires a lot of manual labor
Test executors have to be very careful and meticulous with bookkeeping
14
Run tests on the software and record the results
Software Testing: A Newcomer’s Guide © 2009 15
4. Test Evaluation
This is much harder than it may seem Requires knowledge of :
– Domain– Testing– User interfaces and psychology
Usually requires almost no traditional CS– A background in the domain of the software is essential– An empirical background is very helpful (biology, psychology, …)– A logic background is very helpful (law, philosophy, math, …)
This is intellectually stimulating, rewarding, and challenging– But not to typical CS majors – they want to solve problems and build
things
15
Evaluate results of testing, report to developers
Software Testing: A Newcomer’s Guide © 2009 16
Other Activities Test management : Sets policy, organizes team, interfaces with
development, chooses criteria, decides how much automation is needed, …
Test maintenance : Tests must be saved for reuse as software evolves– Requires cooperation of test designers and automators– Deciding when to trim the test suite is partly policy and partly technical –
and in general, very hard !– Tests should be put in configuration control
Test documentation : All parties participate– Each test must document “why” – criterion and test requirement satisfied
or a rationale for human-designed tests– Traceability throughout the process must be ensured– Documentation must be kept in the automated tests
16
Software Testing: A Newcomer’s Guide © 2009 17
Approximate Number of Personnel A mature test organization may need only one test designer to
work with several test automaters, executors and evaluators Improved automation will reduce the number of test executors
– Theoretically to zero … but not in practice Putting the wrong people on the wrong tasks leads to
inefficiency, low job satisfaction and low job performance– A qualified test designer will be bored with other tasks and look for a job
in development– A qualified test evaluator will not understand the benefits of test criteria
Test evaluators have the domain knowledge, so they must be free to add tests that “blind” engineering processes will not think of
17
Software Testing: A Newcomer’s Guide © 2009 18
Types of Test Activities – Summary
These four general test activities are quite different It is a poor use of resources to use people inappropriately
18
1a. Design Design test values to satisfy engineering goals
Criteria Requires knowledge of discrete math, programming and testing
1b. Design Design test values from domain knowledge and intuition
Human Requires knowledge of domain, UI, testing
2. Automation
Embed test values into executable scripts
Requires knowledge of scripting
3. Execution Run tests on the software and record the results
Requires very little knowledge
4. Evaluation Evaluate results of testing, report to developers
Requires domain knowledge
Most test teams use the same people for ALL FOUR activities !!
Software Testing: A Newcomer’s Guide © 2009 19
Applying Test Activities
19
To use our people effectively
and to test efficiently
we need a process that
lets test designers
raise their level of abstraction
Software Testing: A Newcomer’s Guide © 2009 20
Model-Driven Test Design
20
software
artifact
model / structur
e
test requireme
nts
refined requirement
s / test specs
input values
test cases
test script
s
test result
s
pass / fail
IMPLEMENTATIONABSTRACTION
LEVEL
DESIGNABSTRACTION
LEVEL
Software Testing: A Newcomer’s Guide © 2009 21
Model-Driven Test Design – Steps
21
software
artifact
model / structur
e
test requireme
nts
refined requirement
s / test specs
input values
test cases
test script
s
test result
s
pass / fail
IMPLEMENTATIONABSTRACTION
LEVEL
DESIGNABSTRACTION
LEVEL
analysis
criterion refine
generate
prefixpostfix
expected
automateexecuteevaluate
Software Testing: A Newcomer’s Guide © 2009 22
Model-Driven Test Design – Activities
22
software
artifact
model / structur
e
test requireme
nts
refined requirement
s / test specs
input values
test cases
test script
s
test result
s
pass / fail
IMPLEMENTATIONABSTRACTION
LEVEL
DESIGNABSTRACTION
LEVEL
Test Design
Test Automatio
n
Test Execution
Test Evaluation
Raising our abstraction level makestest design MUCH easier
Software Testing: A Newcomer’s Guide © 2009 23
Software Testing Terms
Like any field, software testing comes with a large number of specialized terms that have particular meanings in this context
Some of the following terms are standardized, some are used consistently throughout the literature and the industry, but some vary by author, topic, or test organization
The definitions here are intended to be the most commonly used
23
Software Testing: A Newcomer’s Guide © 2009 2424
Important TermsValidation & Verification (IEEE)
Validation : The process of evaluating software at the end of software development to ensure compliance with intended usage
Verification : The process of determining whether the products of a given phase of the software development process fulfill the requirements established during the previous phase
IV&V stands for “independent verification and validation”
Software Testing: A Newcomer’s Guide © 2009 2525
Test Engineer & Test Managers Test Engineer : An IT professional who is in charge of one or
more technical test activities– designing test inputs– producing test values– running test scripts– analyzing results– reporting results to developers and managers
Test Manager : In charge of one or more test engineers– sets test policies and processes– interacts with other managers on the project– otherwise helps the engineers do their work
Software Testing: A Newcomer’s Guide © 2009 2626
Test Engineer Activities
Test
Designs
Output
Executable
Tests
Computer EvaluateP
TestManager
TestEngineer
TestEngineer
design instantiate
execute
Software Testing: A Newcomer’s Guide © 2009 2727
Static and Dynamic Testing
Static Testing : Testing without executing the program– This include software inspections and many forms of analysis– Very effective at finding certain kinds of problems – especially “potential” faults,
that is, mistakes that may only be visible after the program evolves– Example faults identifiable with static analysis:
• Overriding equals(), but not hashCode()• Implementing clone() by calling a constructor• Using “foreign” data prior to scrubbing
– Hypertext inputs– Parts of SQL queries– Array indices
Dynamic Testing : Testing by executing the program with real inputs– Mostly what this talk is about
Software Testing: A Newcomer’s Guide © 2009 2828
Software Faults, Errors & Failures
Software Fault : A static defect in the software
Software Error : An incorrect internal state that is the manifestation of some fault
Software Failure : External, incorrect behavior with respect to the requirements or other description of the expected behavior
Faults in software are design mistakes and will always exist
Software Testing: A Newcomer’s Guide © 2009 2929
Testing & Debugging
Testing : Finding inputs that cause the software to fail– The principle topic of this lecture
Debugging : The process of finding a fault given a failure– Fault localization is a huge issue– Some faults have failures that are hard to reproduce– Often desirable to recast a problem report as a “short” test case that also
reveals the failure• General principle: Faults usually have “short” revealing test cases• These test cases are excellent candidates for regression tests
Software Testing: A Newcomer’s Guide © 2009 3030
Fault & Failure Model
Three conditions necessary for a failure to be observed
1. Reachability : The location or locations in the program that contain the fault must be reached
2. Infection : The state of the program must be incorrect
3. Propagation : The infected state must propagate to cause some output of the program to be incorrect
Software Testing: A Newcomer’s Guide © 2009 3131
Test Case
Test Case Values : The values that directly satisfy one test requirement
Expected Results : The result that will be produced when executing the test if the program satisfies it intended behavior
Software Testing: A Newcomer’s Guide © 2009 3232
Observability and Controllability
Software Observability : How easy it is to observe the behavior of a program in terms of its outputs, effects on the environment and other hardware and software components
– Software that affects hardware devices, databases, or remote files have low observability
Software Controllability : How easy it is to provide a program with the needed inputs, in terms of values, operations, and behaviors
– Easy to control software with inputs from keyboards– Inputs from hardware sensors or distributed software is harder– Data abstraction reduces controllability and observability
Software Testing: A Newcomer’s Guide © 2009 3333
Inputs to Affect Controllability and Observability
Prefix Values : Any inputs necessary to put the software into the appropriate state to receive the test case values
Postfix Values : Any inputs that need to be sent to the software after the test case values
Two types of postfix values1. Verification Values : Values necessary to see the results of the test case values2. Exit Commands : Values needed to terminate the program or otherwise return it
to a stable state
Executable Test Script : A test case that is prepared in a form to be executed automatically on the test software and produce a report– Example: Junit tests
Software Testing: A Newcomer’s Guide © 2009 3434
Top-Down and Bottom-Up Testing
Top-Down Testing : Test the main procedure, then go down through procedures it calls, and so on
Bottom-Up Testing : Test the leaves in the tree (procedures that make no calls), and move up to the root.
– Each procedure is not tested until all of its children have been tested
Software Testing: A Newcomer’s Guide © 2009 3535
White-box and Black-box Testing
Black-box testing : Deriving tests from external descriptions of the software, including specifications, requirements, and design
White-box testing : Deriving tests from the source code internals of the software, specifically including branches, individual conditions, and statements
This view is really out of date.The more general question is: from what level of abstraction
to we derive tests?
Software Testing: A Newcomer’s Guide © 2009 3636
Evolving Notion of Coverage Criteria
Old view of testing is of testing at specific software development phases
– Unit, module, integration, system …
New view is in terms of structures and criteria
– Graphs, logical expressions, syntax, input space
Software Testing: A Newcomer’s Guide © 2009 3737
Traditional : Testing at Different Levels
Class A
method mA1()
method mA2()
Class B
method mB1()
method mB2()
main Class P Acceptance testing: Is
the software acceptable to the user?
Integration testing: Test how modules interact with each other
System testing: Test the overall functionality of the system
Module testing: Test each class, file, module or component
Unit testing: Test each unit (method) individually
Software Testing: A Newcomer’s Guide © 2009 3838
Beizer’s Insight : Find a Graph and Cover It Tailored to:
– a particular software artifact• code, design, specifications
– a particular phase of the lifecycle• requirements, specification, design, implementation
But graphs do not characterize all testing techniques well
Four abstract models seem to suffice …
Software Testing: A Newcomer’s Guide © 2009 3939
New : Test Coverage Criteria
g Test Requirements : Specific things that must be satisfied or covered during testing
g Test Criterion : A collection of rules and a process that define test requirements
A tester’s job is simple : Define a model of the software, then find ways to cover it
Testing researchers have defined dozens of criteria, but they are all really just a few criteria on four types of structures …
Software Testing: A Newcomer’s Guide © 2009 4040
New : Criteria Based on Structures
1. Graphs
2. Logical Expressions
3. Input Domain Characterization
4. Syntactic Structures
(not X or not Y) and A and B
if (x > y) z = x - y;else z = 2 * x;
Structures : Four ways to model software
A: {0, 1, >1}B: {600, 700, 800}C: {swe, cs, isa, infs}
Software Testing: A Newcomer’s Guide © 2009 4141
1. Graph Coverage – Structural
6
5
3
2
1 7
4
Node (Statement)
Cover every node
• 12567
• 1343567
This graph may represent• statements & branches• methods & calls• components & signals• states and transitions
Edge (Branch)
Cover every edge
• 12567
• 1343567
• 1357
Path
Cover every path
• 12567
• 1257
• 13567
• 1357
• 1343567
• 134357 …
Software Testing: A Newcomer’s Guide © 2009 4242
Defs & Uses Pairs• (x, 1, (1,2)), (x, 1, (1,3))• (y, 1, 4), (y, 1, 6)• (a, 2, (5,6)), (a, 2, (5,7)),
(a, 3, (5,6)), (a, 3, (5,7)),• (m, 2, 7), (m, 4, 7), (m, 6,
7)
1. Graph Coverage – Data Flow
6
5
3
2
1 7
4This graph contains:• defs: nodes & edges where
variables get values• uses: nodes & edges
where values are accessed
def = {x, y}
def = {a , m}
def = {a}
def = {m}
def = {m}
use = {x}
use = {x}
use = {a}
use = {a}
use = {y}
use = {m}
use = {y}
All Defs
Every def used once
• 1, 2, 5, 6, 7
• 1, 2, 5, 7
• 1, 3, 4, 3, 5, 7
All Uses
Every def “reaches” every use
• 1, 2, 5, 6, 7
• 1, 2, 5, 7
• 1, 3, 5, 6, 7
• 1, 3, 5, 7
• 1, 3, 4, 3, 5,7
Software Testing: A Newcomer’s Guide © 2009 4343
1. Graph - FSM ExampleMemory Seats in a Lexus ES 300
Driver 1Configuration
Driver 2Configuration
[Ignition = off] | Button2
[Ignition = off] | Button1
ModifiedConfiguration
sideMirrors ()[Ignition = on] |
lumbar ()[Ignition = on] |
seatBottom ()[Ignition = on] |
seatBack ()[Ignition = on] |
NewConfiguration
Driver 1
NewConfiguration
Driver 2
[Ignition = on] | Reset AND Button1
[Ignition = on] | Reset AND Button2
Ignition = off
Ignition = off
(to Modified)
Guard (safety constraint) Trigger (input)
Software Testing: A Newcomer’s Guide © 2009 4444
2. Logical Expressions
( (a > b) or G ) and (x < y)
Transitions
Software Specifications
Program Decision StatementsLogical
Expressions
Software Testing: A Newcomer’s Guide © 2009 4545
2. Logical Expressions
Predicate Coverage : Each predicate must be true and false– ( (a>b) or G ) and (x < y) = True, False
Clause Coverage : Each clause must be true and false– (a > b) = True, False– G = True, False– (x < y) = True, False
Combinatorial Coverage : Various combinations of clauses– Active Clause Coverage: Each clause must determine the predicate’s result
( (a > b) or G ) and (x < y)
Software Testing: A Newcomer’s Guide © 2009 4646
2. Logic – Active Clause Coverage or Multiple Condition/Decision Coverage (MCDC)
( (a > b) or G ) and (x < y)
1 T F T
2 F F T
duplicate3 F T T
4 F F T
5 T T T
6 T T F
With these values for G and (x<y), (a>b) determines the value of the predicate
2: Logic Disjunctive Normal Form (DNF) Coverage
Consider the DNF predicate: f = ab + cd For implicant ab
– For a, choose UTP, NFP pair• TTFF, FTFF
– For b, choose UTP, NFP pair• TTFT, TFFT
For implicant cd– For c, choose UTP, NFP pair
• FFTT, FFFT– For d, choose UTP, NFP pair
• FFTT, FFTF Possible CUTPNFP test set
– {TTFF, TTFT, FFTT //UTPs FTFF, TFFT, FFFT, FFTF} //NFPs
01
00
10110100 ab cd
t
t
tt11
10
t
tt
Software Testing: A Newcomer’s Guide © 2009 4848
3. Input Domain Characterization Describe the input domain of the software
– Identify inputs, parameters, or other categorization– Partition each input into finite sets of representative values– Choose combinations of values
System level– Number of students { 0, 1, >1 }– Level of course { 600, 700, 800 }– Major { swe, cs, isa, infs }
Unit level– Parameters F (int X, int Y)– Possible values X: { <0, 0, 1, 2, >2 }, Y : { 10, 20, 30 }– Tests
• F (-5, 10), F (0, 20), F (1, 30), F (2, 10), F (5, 20)
Software Testing: A Newcomer’s Guide © 2009 4949
4. Syntactic Structures Based on a grammar, or other syntactic definition Primary example is mutation testing
1. Induce small changes to the program: mutants2. Find tests that cause the mutant programs to fail: killing mutants3. Failure is defined as different output from the original program4. Check the output of useful tests on the original program
Example program and mutants
if (x > y)
z = x - y;
else
z = 2 * x;
if (x > y)
if (x >= y)
z = x - y;
z = x + y;
z = x – m;
else
z = 2 * x;
Relational Operator Replacement
Arithmetic Operator ReplacementScalar Variable Replacement
Software Testing: A Newcomer’s Guide © 2009 50
Source of Structures
These structures can be extracted from lots of software artifacts– Graphs can be extracted from UML use cases, finite state machines,
source code, …– Logical expressions can be extracted from decisions in program source,
guards on transitions, conditionals in use cases, … Model-based testing derives tests from a model that describes
some aspects of the system under test– The model usually describes part of the behavior– The source is usually not considered a model
50
Software Testing: A Newcomer’s Guide © 2009 5151
Coverage OverviewFour Structures for Modeling Software
Graphs
Logic Input Space
Syntax
Use cases
Specs
Design
Source
Applied to
DNFSpecs
FSMsSource
Applied to
Input
Models
Integ
Source
Applied to
Software Testing: A Newcomer’s Guide © 2009 5252
Coverage
Infeasible test requirements : test requirements that cannot be satisfied
– No test case values exist that meet the test requirements– Dead code– Detection of infeasible test requirements is formally undecidable for most test
criteria
Thus, 100% coverage is impossible in practice
Given a set of test requirements TR for coverage criterion C, a test set T satisfies C coverage if and only if for every test requirement tr in TR, there is at least one test t in T such that t satisfies tr
Software Testing: A Newcomer’s Guide © 2009 5353
Two Ways to Use Test Criteria
1. Directly generate test values to satisfy the criterion often assumed by the research community most obvious way to use criteria very hard without automated tools
2. Generate test values externally and measure against the criterion usually favored by industry– sometimes misleading– if tests do not reach 100% coverage, what does that mean?
Test criteria are sometimes called metrics
Software Testing: A Newcomer’s Guide © 2009 5454
Generators and Recognizers
Generator : A procedure that automatically generates values to satisfy a criterion
Recognizer : A procedure that decides whether a given set of test values satisfies a criterion
Both problems are provably undecidable for most criteria It is possible to recognize whether test cases satisfy a criterion
far more often than it is possible to generate tests that satisfy the criterion
Coverage analysis tools are quite plentiful
Software Testing: A Newcomer’s Guide © 2009 5555
Comparing Criteria with Subsumption
Criteria Subsumption : A test criterion C1 subsumes C2 if and only if every set of test cases that satisfies criterion C1 also satisfies C2
Must be true for every set of test cases Example : If a test set has covered every branch in a program
(satisfied the branch criterion), then the test set is guaranteed to also have covered every statement
Software Testing: A Newcomer’s Guide © 2009 5656
Test Coverage Criteria
Traditional software testing is expensive and labor-intensive Formal coverage criteria are used to decide which test inputs to
use More likely that the tester will find problems Greater assurance that the software is of high quality and
reliability A goal or stopping rule for testing Criteria makes testing more efficient and effective
But how do we start to apply these ideas in practice?
Software Testing: A Newcomer’s Guide © 2009 5757
Part 3 : How ?
How do we get there ?
Now we know why and what …
Software Testing: A Newcomer’s Guide © 2009 5858
Beizer’s Maturity Levels
Level 0 : There’s no difference between testing and debugging
Level 1 : The purpose of testing is to show correctness Level 2 : The purpose of testing is to show that the software
doesn’t work Level 3 : The purpose of testing is not to prove anything specific,
but to reduce the risk of using the software Level 4 : Testing is a mental discipline that helps all IT
professionals develop higher quality software
Software Testing: A Newcomer’s Guide © 2009 5959
Level 0 Thinking
Testing is the same as debugging
Does not distinguish between incorrect behavior and mistakes in the program
Does not help develop software that is reliable or safe
This is what we teach undergraduate CS majors
Software Testing: A Newcomer’s Guide © 2009 6060
Level 1 Thinking
Purpose is to show correctness Correctness is impossible to achieve What do we know if no failures?
– Good software or bad tests?
Test engineers have no:– Strict goal– Real stopping rule– Formal test technique– Test managers are powerless
This is what hardware engineers often expect
Software Testing: A Newcomer’s Guide © 2009 6161
Level 2 Thinking
Purpose is to show failures
Looking for failures is a negative activity
Puts testers and developers into an adversarial relationship
What if there are no failures?
This describes most software companies.
How can we move to a team approach ??
Software Testing: A Newcomer’s Guide © 2009 6262
Level 3 Thinking
Testing can only show the presence of failures
Whenever we use software, we incur some risk
Risk may be small and consequences unimportant
Risk may be great and the consequences catastrophic
Testers and developers work together to reduce risk
This describes a few “enlightened” software companies
Software Testing: A Newcomer’s Guide © 2009 6363
Level 4 Thinking
A mental discipline that increases quality
Testing is only one way to increase quality
Test engineers can become technical leaders of the project
Primary responsibility to measure and improve software quality
Their expertise should help the developers
This is the way “traditional” engineering works
Software Testing: A Newcomer’s Guide © 2009 6464
Summary
More testing saves money– Planning for testing saves lots of money
Testing is no longer an “art form”– Engineers have a tool box of test criteria
When testers become engineers, the product gets better– The developers get better
Software Testing: A Newcomer’s Guide © 2009 6565
Open Questions Which criteria work best on embedded, highly reliable software?
– Which software structure to use?
How can we best automate this testing with robust tools?– Deriving the software structure– Constructing the test requirements– Creating values from test requirements– Creating full test scripts– Solution to the “mapping problem”
Empirical validation Technology transition Application to new domains
Software Testing: A Newcomer’s Guide © 2009 66
Summary of Today’s New Ideas Why do we test – to reduce the risk of using the software Four types of test activities – test design, automation, execution
and evaluation Software terms – faults, failures, the RIP model, observability
and controllability Four structures – test requirements and criteria Test process maturity levels – level 4 is a mental discipline that
improves the quality of the software
66
Earlier and better testing can empower the test manager
Software Testing: A Newcomer’s Guide © 2009 67
Part 4: Testing Topics by ICST Section ICST has 16 Sessions with Papers: 13 Research and 3 Industry
– R1: GUI Testing– R2: Model Checking– R3: Embedded and Real-Time Testing– R4: QA and Test Management– R5: Model-Based Testing– R6: Static Analysis– R7: Security Testing– R8: Empirical Studies– R9: Test Case Generation– R10: Web Testing– R11: Aspects and Faults– R12: Mutation and Non Functional Testing– R13: Assertions and Failure States– I3: Real World Testing– I2: Test Management– I3: Automation
Following slides briefly overview foundations for each Session– Tall Order!– I’ll be brief…
67
Software Testing: A Newcomer’s Guide © 2009 68
Section R1: GUI Testing Basic Issues
– Many systems have only a GUI interface– Problems may exist in GUI, or in underlying application– Structural Tests
• Legal event sequences / hiding of uninteresting events– Model Based Tests
• Operational / Behavioral / Graph models Research Foci
– Case studies on industrial software– Reuse and scalability are huge issues
• Particularly in the presence of maintenance– Crash testing
68
Software Testing: A Newcomer’s Guide © 2009 69
Section R2: Model Checking Basic Issues
– Define a labeled state space with transitions: A state machine– Check (temporal) properties over paths in that state space– Bonus: Counterexamples– Standard Problem: Scalability
Research Foci– Show two descriptions consistent (or identical)– Test case generation
• Interpreting counterexamples as test cases• Using model checker as test generation engine
– Model checking “real” code• Direct application to programs (eg JavaPathFinder)
69
Software Testing: A Newcomer’s Guide © 2009 70
Section R3: Embedded and Real-Time Testing
Basic Issues– Embedded software has a huge observability problem
• How do you know the exact state of the SUT?– Testing timeliness constraints as well as functional correctness
Research Foci– Abstract models for SUT– Notions such as Partial Observability– Passive Testing
• Non interference of test harness with observations– Test specification frameworks for specific domains
• TTCN-3
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Section R4: QA and Test Management Basic Issues
– Scale: How to manage very large artifacts– Comprehensiveness: How to encompass heterogeneous analyses?
Research Foci– In vivo testing of deployed applications
• Contrast with testing in a lab• No “clean slate”
– Flexible frameworks to manage analysis– Dealing with large test suites
• Substantial test set up time required• Contention for test resource between different test tasks
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Section R5: Model-Based Testing Basic Issues
– Test cases are derived from a model of the SUT– Modeling addresses many engineering concerns– Very active research area
Research Foci– Testing real-time systems – when to best schedule a test?– Testing from UML
• Sequence and state machine models– Exploring the link between formal modeling and model-based testing
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Section R6: Static Analysis Basic Issues
– Analyze code without execution– Widely used for identifying vulnerabilities and other flaws
Research Foci– Empirical analysis of effectiveness of static analysis tools
• Fault detection• Refactoring
– Symbolic analysis• Safety analysis for critical software
– Actionable static analysis alerts• Distinguishing false positives from true positives
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Section R7: Security Testing Basic Issues
– Testing intended security functions• Very similar to testing any other type of function
– Testing for unintended behavior• Much harder – focus is on what system does not do
Research Foci– Adapting functional tests to also test intended security functions
• “Separation of concerns” implementations– Predicting which components are attack targets
• Early identification of problem components• Issue of false positives vs. true positives
– Very high level models• Seasonal variations in vulnerability discovery
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Section R8: Empirical Studies Basic Issue
– Empirical studies are crucial foundations for software engineering• Only so much you can do with theorems
Research Foci– Studying automating software testing in large organizations
• What are the factors that lead to success?– Studying capture/recapture models
• Effect of number of natural faults– Studying redundancy in test cases
• Basis for reducing test sets such as regression sets
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Section R9: Test Case Generation Basic Issues
– Old, but very important problem– We need tools that can automatically generate good test data!
Research Foci– Generating feasible paths in finite state machines
• Hard problem whether a given transition is, in fact, feasible– Generating test inputs to follow paths
• Key factors– Constraint solving– Path explosion– Relation of paths to other coverage goals
– Test inputs to satisfy complex predicates• Efficient algorithms
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Section R10: Web Testing Basic Issues
– Web testing is large, complex issue– Reliability requirements are very high
• Customers simply click away from unreliable web applications Research Foci
– Testing tools for web services• Data driven test generation
– Taking advantage of user session data• Identifying key relationships by observing actual behavior
– Penetration testing• By definition, every web application is a potential target• Key: Find vulnerabilities in web applications before the bad guys
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Section R11: Aspects and Faults Basic Issues
– Very disparate session• Logic faults, fault localization, and aspect-oriented programming!
Research Foci– Minimizing the size of fault-detecting test sets (logic testing)
• Analyzing infeasible test requirements• Making sure every test has a reason for being in the set
– Tracing failed test cases back to faults• Probabilistic distributions of faults
– Aspect-Oriented programming• Using test cases to drive pointcut descriptors
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Section R12: Mutation and Non Functional Testing
Basic Issues– Mutation testing is a powerful approach to testing
• Goal is a test set sensitive enough to detect all mutants• Mutants used as source for seeded faults
– Testing nonfunctional properties such as response time and security Research Foci
– Mutation testing for logic expressions• New mutation operators with much more powerful mutants
– Revived research interest in Higher-Order Mutants (HOMs)– Mutation testing of database applications
• Goal: Test databases “rich” enough to detect query faults– Testing component-based distributed systems
• Widespread applications demand effective approaches
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Section R13: Assertions and Failure States Basic Issues
– Assertions are statements that must be true at given points in execution• Extremely powerful approach to fault detection
– Failure states are program states after something bad happens. Research Foci
– Extracting tests from runtime failures• Automatically turning any failure (in operation) into a test• Huge potential practical impact• Clearly, overhead needs to be low
– Assertion-based test validation• When software is modified, which assertions need to be checked?
– Metamorphic testing• Solving the “oracle” problem by relating multiple program “runs”• Experience with implementing this approach via assertions
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Section I1: Real World Testing Basic Issue
– Testability:• The degree to which components are easy to test
– Components can be designed to be easier to test• The efficiency of the test process
Research Foci– Why testability is hard in practice
• Organizational factors• Technical Factors
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Section I2: Test Management Basic Issues
– How to plan for test phase of a project– How to optimize test resources
Research Foci– Estimating test effort based on use cases
• Case study with comparison to other approaches– Estimating test effort for functional test cases
• Case study– Regression set selection
• Which tests need to be rerun• Evaluation on large industrial system
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Section I3: Automation Basic Issues
– Test generation– Code for multi-core processors– Specialized languages
Research Foci– Test generation to satisfy coverage criteria
• Application to safety critical system– How to test code optimized for multi-core?
• Testing multi-threaded is much harder than single-threaded!– Developing high level languages for specific domains
• High level test approaches are a necessary complement
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