Module-5 Integration testing and System Testing.pdf

Ch 21, slide 1
Integration and Component-based Software
Testing
6/28/2023

Ch 21, slide 2
Learning objectives
• Understand the purpose of integration testing
– Distinguish typical integration faults from faults that should be
eliminated in unit testing
– Understand the nature of integration faults and how to prevent
as well as detect them
• Understand strategies for ordering construction and
testing
– Approaches to incremental assembly and testing to reduce
effort and control risk
• Understand special challenges and approaches for
testing component-based systems
6/28/2023

What is integration testing?
Module test Integration test System test
Specification: Module
interface
Interface specs,
module breakdown
Requirements
specification
Visible
structure:
Coding details Modular structure
(software
architecture)
— none —
Scaffolding
required:
Some Often extensive Some
Looking for
faults in:
Modules Interactions,
compatibility
System
functionality
Ch 21, slide 3
6/28/2023

Integration versus Unit Testing
• Unit (module) testing is a necessary foundation
– Unit level has maximum controllability and visibility
– Integration testing can never compensate for inadequate unit
testing
• Integration testing may serve as a process check
– If module faults are revealed in integration testing, they signal
inadequate unit testing
– If integration faults occur in interfaces between correctly
implemented modules, the errors can be traced to module
breakdown and interface specifications
Ch 21, slide 4
6/28/2023

Ch 21, slide 5
Integration Faults
• Inconsistent interpretation of parameters or values
– Example: Mixed units (meters/yards) in Martian Lander
• Violations of value domains, capacity, or size limits
– Example: Buffer overflow
• Side effects on parameters or resources
– Example: Conflict on (unspecified) temporary file
• Omitted or misunderstood functionality
– Example: Inconsistent interpretation of web hits
• Nonfunctional properties
– Example: Unanticipated performance issues
• Dynamic mismatches
– Example: Incompatible polymorphic method calls
6/28/2023

Ch 21, slide 6
Example: A Memory Leak
Apache web server, version 2.0.48
Response to normal page request on secure (https) port
static void ssl io filter disable(ap filter t *f)
{ bio filter in ctx t *inctx = f->ctx;
inctx->ssl = NULL;
inctx->filter ctx->pssl = NULL;
}
No obvious error, but
Apache leaked memory
slowly (in normal use) or
quickly (if exploited for a
DOS attack)
6/28/2023

Ch 21, slide 7
SSL_free(inctx -> ssl);
inctx->ssl = NULL;
}
The missing code is for a
structure defined and
created elsewhere,
accessed through an
opaque pointer.
6/28/2023

Ch 21, slide 8
SSL_free(inctx -> ssl);
inctx->ssl = NULL;
}
Almost impossible to find
with unit testing.
(Inspection and some
dynamic techniques could
have found it.)
6/28/2023

Maybe you’ve heard ...
• Yes, I implemented
module A , but I didn’t
test it thoroughly yet. It
will be tested along with
module B when that’s
ready.
Ch 21, slide 10
6/28/2023

Translation...
• Yes, I implemented
module A , but I didn’t
test it thoroughly yet. It
will be tested along with
module B when that’s
ready.
• I didn’t think at all about
the strategy for testing. I
didn’t design module
A for testability and I
didn’t think about the best
order to build and test
modules A and B .
Ch 21, slide 11
6/28/2023

System Architecture
Integration Plan + Test Plan
• Integration test
plan drives and is
driven by the
project “build
plan”
– A key feature of
the system
architecture and
project plan
Ch 21, slide 12
Build Plan
...
...
Test Plan
...
6/28/2023

Ch 21, slide 13
Big Bang Integration Test
An extreme and desperate approach:
Test only after integrating all modules
+Does not require scaffolding
• The only excuse, and a bad one
- Minimum observability, diagnosability, efficacy, feedback
- High cost of repair
• Recall: Cost of repairing a fault rises as a function of time
between error and repair
6/28/2023

Structural and Functional Strategies
• Structural orientation:
Modules constructed, integrated and tested based on a
hierarchical project structure
– Top-down, Bottom-up, Sandwich, Backbone
• Functional orientation:
Modules integrated according to application
characteristics or features
– Threads, Critical module
Ch 21, slide 14
6/28/2023

Integration testing approaches
Common approaches to perform system
integration testing
 Incremental
 Top-down
 Bottom-up
 Sandwich
 Big-bang
6/28/2023 Ch 21, slide 15

DriversandStubs
 A program that calls the interface procedures of the
module being tested and reports the results. A driver
simul at e s a mo du l e t h a t c a l l s t h e m o d u l e
currently being Tested.
Driver:
Stub:
 A program that has the same interface
procedures as a module that is being
called by the module being tested but is
simpler.
 A stub simulates a module called by the
module currently being tested
Driver
Tested
Unit
Stub
Procedure
call
Procedure
call
Module under test
6/28/2023 Ch 21, slide 16

Example: A3-Layer-Design(SpreadSheet)
Layer I
Layer II
Layer III
Spread
SheetView
Calculator
BinaryFile
Storage
XMLFile
Storage
Currency
DataBase
Currency
Converter
Data
Model
A
C
E F G
D
B
Spread
SheetView
BinaryFile
Storage
Entity
Model
A
E F
Currency
DataBase
G
Currency
Converter
D
B
Calculator
C
XMLFile
Storage
6/28/2023 Ch 21, slide 17

Big-BangApproach
A
C
E F G
D
B
Test A
Test B
Test F
Test G
Test E
Test C
Test D
Test
A, B, C, D,
E, F, G
6/28/2023 Ch 21, slide 18

Bottom-up Testing Strategy
 The subsystems in the lowest layer of the call hierarchy are
tested individually
 Then the next subsystems are tested that call the
previously tested subsystems
 This is repeated until all subsystems are included
 Drivers are needed.
6/28/2023 Ch 21, slide 19

Bottom-up Testing Strategy
A
C
E F G
D
B
A
Test
A, B, C, D,
E, F, G
E
Test E
F
Test F
B
Test B, E, F
C
Test C
D
Test D,G
G
Test G
6/28/2023 Ch 21, slide 20

Pros and Cons of Bottom-Up Integration Testing
Con:
 Tests the most important subsystem (user
interface) last,
 Drivers needed.
Pro:
 No stubs needed.
 Useful for integration testing of the following
systems,
• Object-oriented systems,
• Real-time systems,
• Systems with strict performance
requirements.
6/28/2023 Ch 21, slide 21

Top-down testing strategy
Test the top layer or the controlling subsystem first
Then combine all the subsystems that are called by the
tested subsystems and test the resulting collection of
subsystems
Do this until all subsystems are incorporated into the test
Stubs are needed to do the testing.
6/28/2023 Ch 21, slide 22

T
op-downIntegration
Test
A, B, C, D,
E, F, G
All Layers
Layer I + II
Test A, B, C, D
Layer I
Test A
A
E F
B C D
G
6/28/2023 Ch 21, slide 23

Pros and Cons of Top-down Integration Testing
Pro
 Test cases can be defined in terms of the functionality of
the system
(functional requirements)
 No drivers needed
Cons
 Writing stubs is difficult: Stubs must allow all possible
conditions to be tested.
 Large number of stubs may be required, especially if the
lowest level of the
system contains many methods.
 Some interfaces are not tested separately.
6/28/2023 Ch 21, slide 24

Sandwich Testing Strategy
 Combines top-down strategy with
bottom-up strategy
 The system is viewed as having three
layers
 A target layer in the middle
 A layer above the target
 A layer below the target
 Testing converges at the target layer.
6/28/2023 Ch 21, slide 25

Sandwich Testing Strategy
Test
A, B, C, D,
E, F, G
Test B, E, F
Test D,G
Test A
Test E
Test F
Test G
Test A,B,C, D
A
E F
B C D
G
6/28/2023 Ch 21, slide 26

Pros and Cons of Sandwich Testing
 Top and Bottom Layer Tests can be done in parallel
 Problem: Does not test the individual subsystems
and their
interfaces thoroughly before integration
 Solution: Modified sandwich
6/28/2023 Ch 21, slide 27

Modified SandwichT
estingStrategy
Test in parallel:
 Middle layer with drivers and stubs
 Top layer with stubs
 Bottom layer with drivers
Test in parallel:
 Top layer accessing middle layer (top layer
replaces drivers)
 Bottom accessed by middle layer
(bottom layer replaces stubs).
6/28/2023 Ch 21, slide 28

Modified SandwichT
esting
Test F
Test E
Test B
Test A
Test C
Test B, E, F
Test D
Test D,G
Test G
Test A,C
Test
A, B, C, D,
E, F, G
A
E F
B C D
G
6/28/2023 Ch 21, slide 29

ContinuousT
esting
Continuous build:
Build from day
one Test from
day one
Integrate from day one
 System is always runnable
Requires integrated tool support:
Continuous build server
Automated tests with high
coverage Tool supported
refactoring
Software configuration
management Issue tracking.
6/28/2023 Ch 21, slide 30

ContinuousT
estingStrategy
aryFile
orage
Bin
St
Data
Model
Sp
re
Sheet
V
ad
ie
w
Layer I
Layer II
Layer III
A
E F
Currency
DataBase
G
Currency
Converter
D
B C
Calculator
XMLFile
Storage
Sheet View
+ Cells
+ Addition
+ File Storage
6/28/2023 Ch 21, slide 31

Stepsin IntegrationTesting
4.Test subsystem decomposition: Define test
cases
that exercise all dependencies
5.Test non-functional requirements:
Execute
performance tests
6.Keep records of the test cases and testing
activities.
7.Repeat steps 1 to 7 until the full system
is tested.
The primary goal of integration testing is
to identify failures with the (current)
component configuration.
1.Based on the integration
strategy, select a
component to be tested.
Unit test all the classes in
the component.
2.Put selected component
together; do any
preliminary fix-up
necessary to make the
integration test
operational (drivers, stubs)
3.Test functional
requirements: Define test
cases that exercise all
uses cases with the
selected component
6/28/2023 32/20

QuickTimeª and a
None decompressor
are needed to see this picture.
Top
A C
X
Thread ...
Ch 21, slide 33
A “thread” is a portion of several
modules that together provide a
user-visible program feature.
6/28/2023

QuickTimeª and a
None decompressor
Top
A B C
Y
X
Thread ...
Ch 21, slide 34
Integrating one
thread, then another,
etc., we maximize
visibility for the user
6/28/2023

Thread ...
Ch 21, slide 35
QuickTimeª and a
None decompressor
Top
A B C
Y
X
As in sandwich
integration testing,
we can minimize
stubs and drivers, but
the integration plan
may be complex
6/28/2023

Critical Modules
• Strategy: Start with riskiest modules
– Risk assessment is necessary first step
– May include technical risks (is X feasible?), process risks (is
schedule for X realistic?), other risks
• May resemble thread or sandwich process in tactics for
flexible build order
– E.g., constructing parts of one module to test functionality in
another
• Key point is risk-oriented process
– Integration testing as a risk-reduction activity, designed to
deliver any bad news as early as possible Ch 21, slide 36
6/28/2023

Ch 21, slide 37
Choosing a Strategy
• Functional strategies require more planning
– Structural strategies (bottom up, top down, sandwich) are
simpler
– But thread and critical modules testing provide better process
visibility, especially in complex systems
• Possible to combine
– Top-down, bottom-up, or sandwich are reasonable for relatively
small components and subsystems
– Combinations of thread and critical modules integration testing
are often preferred for larger subsystems
6/28/2023

Integration test metrics
 The number of integration tests for a decomposition tree is the
following
Sessions = nodes – leaves + edges
 For SATM have 42 integration test sessions, which
correspond to 42 separate sets of test cases
 For top-down integration nodes – 1 stubs are needed
 For bottom-up integration nodes – leaves drivers are
needed
 For SATM need 32 stubs and 10 drivers

Call Graph-Based Integration
 The basic idea is to use the call graph instead of the
decomposition tree
 The call graph is a directed, labeled graph
 Vertices are program units; e.g. methods
 A directed edge joins calling vertex to the called
vertex
 Adjacency matrix is also used
 Do not scale well, although some insights are
useful
 Nodes of high degree are critical

Functional decomposition of Calendar Problem

Call Graph
6/28/2023 Ch 21, slide 41

Call graph integration strategies
 Two types of call graph-based integration testing
 Pair-wise Integration Testing
 Neighborhood Integration Testing

Pair-Wise Integration
 The idea behind Pair-Wise integration testing
 Eliminate need for developing stubs / drivers
 Use actual code instead of stubs/drivers
 In order not to deteriorate the process to a big-bang strategy
 Restrict a testing session to just a pair of units in the
call graph.
 Results in one integration test session for each edge
in the call graph.

Pairwise Integration example
6/28/2023 Ch 21, slide 44

Neighbourhood integration
 The neighbourhood of a node in a graph
 The set of nodes that are one edge away
from the given node
 In a directed graph
 All the immediate predecessor nodes and all the
immediate successor nodes of a given node.
 Neighborhood Integration Testing
 Reduces the number of test sessions.
 Fault isolation is more difficult.

Neighborhood Integration Example
6/28/2023 Ch 21, slide 46

Pros and Cons of Call-Graph Integration
 Aim to eliminate / reduce the need for drivers / stubs
 Development effort is a drawback
 Closer to a build sequence
 Neighborhoods can be combined to create “villages”
 Suffer from fault isolation problems
 Specially for large neighborhoods

Pros and Cons of Call-Graph Integration – 2
 Redundancy
 Nodes can appear in several neighborhoods
 Assumes that correct behaviour follows from correct units
and correct interfaces
 Not always the case
 Call-graph integration is well suited to devising a sequence
of builds with which to implement a system

Path-Based Integration
 Motivation
 Combine structural and behavioral type of testing
for integration testing as we did for unit testing.
 Basic idea
 Focus on interactions among system units
 Rather than merely to test interfaces among
separately developed and tested units
 Interface-based testing is structural while interaction-based is
behavioral

Extended Concepts – 1
 Source node
 A program statement fragment at which program
execution begins or resumes.
 For example, the first “begin” statement in a program.
 Also, immediately after nodes that transfer
control to other units.
 Sink node
 A statement fragment at which program execution
terminates.
 The final “end” in a program as well as statements
that transfer control to other units.

Extended Concepts – 2
 Module execution path
 A sequence of statements that begins with a source
node and ends with a sink node with no intervening
sink nodes.
 Message
 A programming language mechanism by which one
unit transfers control to another unit.
 Usually interpreted as subroutine invocations
 The unit which receives the message always returns
control to the message source.

MM-Path
 An interleaved sequence of module execution paths and
messages.
 Describes sequences of module execution paths that include
transfers of control among separate units.
 MM-paths always represent feasible execution paths, and these
paths cross unit boundaries.
 There is no correspondence between MM-paths and DD- paths.
 The intersection of a module execution path with a unit is the
analog of a slice with respect to the MM-path function

MM-Path Example
Source nodes
Sink nodes
Module Execution Paths
MEP(B,2) = <3, 4>
MEP(B,1) = <1, 2>
INT–54
MM-path
MEP(A,1) = <1, 2, 3, 6>
MEP(A,2) = <1, 2, 4>
MEP(A,3) = <5, 6>
MEP(C,2) = <1, 3, 4, 5>
MEP(C,2) = <1, 3, 4, 5>

MM-path Graph
 Given a set of units their MM-path graph is the
directed graph in which
 Nodes are module execution paths
 Edges correspond to messages and returns
from one unit to another
 The definition is with respect to a set of units
 It directly supports composition of units and
composition- based integration testing

MM-path graph example
MEP(C,2)
MEP(A,1)
MEP(A,2)
MEP(B,1)
MEP(C,1)
MEP(B,2)
MEP(A,3)
Solid lines indicate messages (calls)
Dashed lines indicate returns from calls

MM-path guidelines
 How long, or deep, is an MM-path? What determines the end points?
 Message quiescence
 Occurs when a unit that sends no messages is reached
 Module C in the example
 Data quiescence
 Occurs when a sequence of processing ends in the
creation of stored data that is not immediately used
(path D1 and D2)
 Quiescence points are natural endpoints for MM-paths

MM-Path metric
 How many MM-paths are sufficient to test a system
 Should cover all source-to-sink paths in the set of units
 What about loops?
 Use condensation graphs to get directed acyclic graphs
 Avoids an excessive number of paths

Pros and cons of path-based integration
 Hybrid of functional and structural testing
 Functional – represent actions with input and output
 Structural – how they are identified
 Avoids pitfall of structural testing (???)
 Fairly seamless union with system testing
 Path-based integration is closely coupled with actual system
behaviour
 Works well with OO testing
 No need for stub and driver development
 There is a significant effort involved in identifying MM-paths

MM-path compared to other methods
Strategy Ability to test
interfaces
Ability to test
co-functionality
Fault isolation
resolution
Functional
decomposition
Acceptable, can
be deceptive
Limited to pairs
of units
Good to faulty
unit
Call-graph Acceptable Limited to pairs
of units
Good to faulty
unit
MM-path Excellent Complete Excellent to unit
path level

Working Definition of Component
• Reusable unit of deployment and composition
– Deployed and integrated multiple times
– Integrated by different teams (usually)
• Component producer is distinct from component user
• Characterized by an interface or contract
• Describes access points, parameters, and all functional and non-
functional behavior and conditions for using the component
• No other access (e.g., source code) is usually available
• Often larger grain than objects or packages
– Example: A complete database system may be a component
Ch 21, slide 62
6/28/2023

Components — Related Concepts
• Framework
• Skeleton or micro-architecture of an application
• May be packaged and reused as a component, with “hooks” or “slots”
in the interface contract
• Design patterns
• Logical design fragments
• Frameworks often implement patterns, but patterns are not frameworks.
Frameworks are concrete, patterns are abstract
• Component-based system
• A system composed primarily by assembling components, often
“Commercial off-the-shelf” (COTS) components
• Usually includes application-specific “glue code” Ch 21, slide 63
6/28/2023

Component Interface Contracts
• Application programming interface (API) is distinct from
implementation
– Example: DOM interface for XML is distinct from many possible
implementations, from different sources
• Interface includes everything that must be known to use
the component
– More than just method signatures, exceptions, etc
– May include non-functional characteristics like performance,
capacity, security
– May include dependence on other components
Ch 21, slide 64
6/28/2023

Challenges in Testing Components
• The component builder’s challenge:
– Impossible to know all the ways a component may be used
– Difficult to recognize and specify all potentially important
properties and dependencies
• The component user’s challenge:
– No visibility “inside” the component
– Often difficult to judge suitability for a particular use and context
Ch 21, slide 65
6/28/2023

Testing a Component: Producer View
• First: Thorough unit and subsystem testing
– Includes thorough functional testing based on application
program interface (API)
– Rule of thumb: Reusable component requires at least twice the
effort in design, implementation, and testing as a subsystem
constructed for a single use (often more)
• Second: Thorough acceptance testing
– Based on scenarios of expected use
– Includes stress and capacity testing
• Find and document the limits of applicability
Ch 21, slide 66
6/28/2023

Testing a Component: User View
• Not primarily to find faults in the component
• Major question: Is the component suitable for this
application?
– Primary risk is not fitting the application context:
• Unanticipated dependence or interactions with environment
• Performance or capacity limits
• Missing functionality, misunderstood API
– Risk high when using component for first time
• Reducing risk: Trial integration early
– Often worthwhile to build driver to test model scenarios, long
before actual integration Ch 21, slide 67
6/28/2023

Adapting and Testing a Component
• Applications often access components
through an adaptor, which can also be
used by a test driver Ch 21, slide 68
QuickTimeª and a
None decompressor
Component
Adaptor
Application
6/28/2023

Ch 21, slide 69
Summary
• Integration testing focuses on interactions
– Must be built on foundation of thorough unit testing
– Integration faults often traceable to incomplete or
misunderstood interface specifications
• Prefer prevention to detection, and make detection easier by imposing
design constraints
• Strategies tied to project build order
– Order construction, integration, and testing to reduce cost or
risk
• Reusable components require special care
– For component builder, and for component user
6/28/2023

Ch 22, slide 1
System, Acceptance, and Regression
Testing

Ch 22, slide 2
Learning objectives
• Distinguish system and acceptance testing
– How and why they differ from each other and from unit and
integration testing
• Understand basic approaches for quantitative
assessment (reliability, performance, ...)
• Understand interplay of validation and verification for
usability and accessibility
– How to continuously monitor usability from early design to
delivery
• Understand basic regression testing approaches
– Preventing accidental changes

Ch 22, slide 3
System Acceptance Regression
Test for ... Correctness,
completion
Usefulness,
satisfaction
Accidental
changes
Test by ... Development
test group
Test group with
users
Development
test group
Verification Validation Verification

System testing
22.2
Ch 22, slide 4

System Testing
• Key characteristics:
– Comprehensive (the whole system, the whole spec)
– Based on specification of observable behavior
Verification against a requirements specification, not validation, and not opinions
– Independent of design and implementation
Independence: Avoid repeating software design errors in
system test design
Ch 22, slide 5

Independent V&V
• One strategy for maximizing independence: System (and
acceptance) test performed by a different organization
– Organizationally isolated from developers (no pressure to say
“ok”)
– Sometimes outsourced to another company or agency
• Especially for critical systems
• Outsourcing for independent judgment, not to save money
• May be additional system test, not replacing internal V&V
– Not all outsourced testing is IV&V
• Not independent if controlled by development organization
Ch 22, slide 6

Independence without changing staff
• If the development organization controls system testing ...
– Perfect independence may be unattainable, but we can reduce
undue influence
• Develop system test cases early
– As part of requirements specification, before major design
decisions have been made
• Agile “test first” and conventional “V model” are both examples of
designing system test cases before designing the implementation
• An opportunity for “design for test”: Structure system for critical system
testing early in project
Ch 22, slide 7

Incremental System Testing
• System tests are often used to measure progress
– System test suite covers all features and scenarios of use
– As project progresses, the system passes more and more
system tests
• Assumes a “threaded” incremental build plan: Features
exposed at top level as they are developed
Ch 22, slide 8

Global Properties
• Some system properties are inherently global
– Performance, latency, reliability, ...
– Early and incremental testing is still necessary, but provide only
estimates
• A major focus of system testing
– The only opportunity to verify global properties against actual
system specifications
– Especially to find unanticipated effects, e.g., an unexpected
performance bottleneck
Ch 22, slide 9

Context-Dependent Properties
• Beyond system-global: Some properties depend on the
system context and use
– Example: Performance properties depend on environment and
configuration
– Example: Privacy depends both on system and how it is used
• Medical records system must protect against unauthorized use, and
authorization must be provided only as needed
– Example: Security depends on threat profiles
• And threats change!
• Testing is just one part of the approach
Ch 22, slide 10

Establishing an Operational Envelope
• When a property (e.g., performance or real-time
response) is parameterized by use ...
– requests per second, size of database, ...
• Extensive stress testing is required
– varying parameters within the envelope, near the bounds, and
beyond
• Goal: A well-understood model of how the property varies
with the parameter
– How sensitive is the property to the parameter?
– Where is the “edge of the envelope”?
– What can we expect when the envelope is exceeded?
Ch 22, slide 11

Stress Testing
• Often requires extensive simulation of the execution
environment
– With systematic variation: What happens when we push the
parameters? What if the number of users or requests is 10
times more, or 1000 times more?
• Often requires more resources (human and machine)
than typical test cases
– Separate from regular feature tests
– Run less often, with more manual control
– Diagnose deviations from expectation
• Which may include difficult debugging of latent faults! Ch 22, slide 12

Acceptance testing
22.3
Ch 22, slide 13

Estimating Dependability
• Measuring quality, not searching for faults
– Fundamentally different goal than systematic testing
• Quantitative dependability goals are statistical
– Reliability
– Availability
– Mean time to failure
– ...
• Requires valid statistical samples from operational profile
– Fundamentally different from systematic testing
Ch 22, slide 14

Statistical Sampling
• We need a valid operational profile (model)
– Sometimes from an older version of the system
– Sometimes from operational environment (e.g., for an
embedded controller)
– Sensitivity testing reveals which parameters are most important,
and which can be rough guesses
• And a clear, precise definition of what is being measured
– Failure rate? Per session, per hour, per operation?
• And many, many random samples
– Especially for high reliability measures
Ch 22, slide 15

Is Statistical Testing Worthwhile?
• Necessary for ...
– Critical systems (safety critical, infrastructure, ...)
• But difficult or impossible when ...
– Operational profile is unavailable or just a guess
• Often for new functionality involving human interaction
– But we may factor critical functions from overall use to obtain a good model of
only the critical properties
– Reliability requirement is very high
• Required sample size (number of test cases) might require years of
test execution
• Ultra-reliability can seldom be demonstrated by testing
Ch 22, slide 16

Process-based Measures
• Less rigorous than statistical testing
– Based on similarity with prior projects
• System testing process
– Expected history of bugs found and resolved
• Alpha, beta testing
– Alpha testing: Real users, controlled environment
– Beta testing: Real users, real (uncontrolled) environment
– May statistically sample users rather than uses
– Expected history of bug reports
Ch 22, slide 17

Usability
22.4
Ch 22, slide 18

Usability
• A usable product
– is quickly learned
– allows users to work efficiently
– is pleasant to use
• Objective criteria
– Time and number of operations to perform a task
– Frequency of user error
• blame user errors on the product!
• Plus overall, subjective satisfaction
Ch 22, slide 19

Verifying Usability
• Usability rests ultimately on testing with real users —
validation, not verification
– Preferably in the usability lab, by usability experts
• But we can factor usability testing for process visibility —
validation and verification throughout the project
– Validation establishes criteria to be verified by testing, analysis,
and inspection
Ch 22, slide 20

Factoring Usability Testing
Validation
(usability lab)
• Usability testing
establishes usability
check-lists
– Guidelines applicable
across a product line or
domain
• Early usability testing
evaluates “cardboard
prototype” or mock-up
Verification
(developers, testers)
• Inspection applies
usability check-lists to
specification and design
• Behavior objectively
verified (e.g., tested)
against interface design
Ch 22, slide 21

Varieties of Usability Test
• Exploratory testing
– Investigate mental model of users
– Performed early to guide interface design
• Comparison testing
– Evaluate options (specific interface design choices)
– Observe (and measure) interactions with alternative interaction
patterns
• Usability validation testing
– Assess overall usability (quantitative and qualitative)
– Includes measurement: error rate, time to complete Ch 22, slide 22

Typical Usability Test Protocol
Select representative sample of user groups
– Typically 3-5 users from each of 1-4 groups
– Questionnaires verify group membership
Ask users to perform a representative sequence of tasks
Observe without interference (no helping!)
– The hardest thing for developers is to not help. Professional
usability testers use one-way mirrors.
Measure (clicks, eye movement, time, ...) and follow up with
questionnaire
Ch 22, slide 23

Accessibility Testing
• Check usability by people with disabilities
– Blind and low vision, deaf, color-blind, ...
• Use accessibility guidelines
– Direct usability testing with all relevant groups is usually
impractical; checking compliance to guidelines is practical and
often reveals problems
• Example: W3C Web Content Accessibility Guidelines
– Parts can be checked automatically
– but manual check is still required
• e.g., is the “alt” tag of the image meaningful?
Ch 22, slide 24

Regression Testing
22.5–22.7
Ch 22, slide 25

Regression
• Yesterday it worked, today it doesn’t
– I was fixing X, and accidentally broke Y
– That bug was fixed, but now it’s back
• Tests must be re-run after any change
– Adding new features
– Changing, adapting software to new conditions
– Fixing other bugs
• Regression testing can be a major cost of software
maintenance
– Sometimes much more than making the change Ch 22, slide 26

Basic Problems of Regression Test
• Maintaining test suite
– If I change feature X, how many test cases must be revised
because they use feature X?
– Which test cases should be removed or replaced? Which test
cases should be added?
• Cost of re-testing
– Often proportional to product size, not change size
– Big problem if testing requires manual effort
• Possible problem even for automated testing, when the test suite and
test execution time grows beyond a few hours
Ch 22, slide 27

Test Case Maintenance
• Some maintenance is inevitable
– If feature X has changed, test cases for feature X will require
updating
• Some maintenance should be avoided
– Example: Trivial changes to user interface or file format should
not invalidate large numbers of test cases
• Test suites should be modular!
– Avoid unnecessary dependence
– Generating concrete test cases from test case specifications
can help
Ch 22, slide 28

Obsolete and Redundant
• Obsolete: A test case that is not longer valid
– Tests features that have been modified, substituted, or removed
– Should be removed from the test suite
• Redundant: A test case that does not differ significantly
from others
– Unlikely to find a fault missed by similar test cases
– Has some cost in re-execution
– Has some (maybe more) cost in human effort to maintain
– May or may not be removed, depending on costs
Ch 22, slide 29

Selecting and Prioritizing Regression Test Cases
• Should we re-run the whole regression test suite? If so,
in what order?
– Maybe you don’t care. If you can re-rerun everything
automatically over lunch break, do it.
– Sometimes you do care ...
• Selection matters when
– Test cases are expensive to execute
• Because they require special equipment, or long run-times, or cannot
be fully automated
• Prioritization matters when
– A very large test suite cannot be executed every day Ch 22, slide 30

Code-based Regression Test Selection
• Observation: A test case can’t find a fault in code it
doesn’t execute
– In a large system, many parts of the code are untouched by
many test cases
• So: Only execute test cases that execute changed or new
code
Ch 22, slide 31
QuickTimeª and a
None decompressor
QuickTimeª and a
None decompressor
QuickTimeª and a
None decompressor
New or changed
Executed by
test case

Control-flow and Data-flow Regression Test Selection
• Same basic idea as code-based selection
– Re-run test cases only if they include changed elements
– Elements may be modified control flow nodes and edges, or
definition-use (DU) pairs in data flow
• To automate selection:
– Tools record elements touched by each test case
• Stored in database of regression test cases
– Tools note changes in program
– Check test-case database for overlap
Ch 22, slide 32

Specification-based Regression Test Selection
• Like code-based and structural regression test case
selection
– Pick test cases that test new and changed functionality
• Difference: No guarantee of independence
– A test case that isn’t “for” changed or added feature X might
find a bug in feature X anyway
• Typical approach: Specification-based prioritization
– Execute all test cases, but start with those that related to
changed and added features
Ch 22, slide 33

Prioritized Rotating Selection
• Basic idea:
– Execute all test cases, eventually
– Execute some sooner than others
• Possible priority schemes:
– Round robin: Priority to least-recently-run test cases
– Track record: Priority to test cases that have detected faults
before
• They probably execute code with a high fault density
– Structural: Priority for executing elements that have not been
recently executed
• Can be coarse-grained: Features, methods, files, ... Ch 22, slide 34

Ch 22, slide 35
Summary
• System testing is verification
– System consistent with specification?
– Especially for global properties (performance, reliability)
• Acceptance testing is validation
– Includes user testing and checks for usability
• Usability and accessibility require both
– Usability testing establishes objective criteria to verify
throughout development
• Regression testing repeated after each change
– After initial delivery, as software evolves

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