Software Testing Strategies lecture .ppt

1
 Software Testing Strategies
Slide Set to accompany
Software Engineering: A Practitioner’s Approach, 7/e
by Roger S. Pressman
Slides copyright © 1996, 2001, 2005, 2009 by Roger S. Pressman
For non-profit educational use only
May be reproduced ONLY for student use at the university level when used in conjunction
with Software Engineering: A Practitioner's Approach, 7/e. Any other reproduction or use is
prohibited without the express written permission of the author.
All copyright information MUST appear if these slides are posted on a website for student
use.

2
Software Testing
Testing is the process of exercising
a program with the specific intent of
finding errors prior to delivery to the
end user.

3
What Testing Shows
errors
errors
requirements conformance
requirements conformance
performance
performance
an indication
an indication
of quality
of quality

4
Strategic Approach
 To perform effective testing, you should conduct
effective technical reviews. By doing this, many errors
will be eliminated before testing commences.
 Testing begins at the component level and works
"outward" toward the integration of the entire
computer-based system.
 Different testing techniques are appropriate for different
software engineering approaches and at different points
in time.
 Testing is conducted by the developer of the software
and (for large projects) an independent test group.
 Testing and debugging are different activities, but
debugging must be accommodated in any testing
strategy.

5
V & V
 Verification refers to the set of tasks that ensure
that software correctly implements a specific
function.
 Validation refers to a different set of tasks that
ensure that the software that has been built is
traceable to customer requirements. Boehm
[Boe81] states this another way:
 Verification: "Are we building the product right?"
 Validation: "Are we building the right product?"

6
Who Tests the Software?
developer
developer independent tester
independent tester
Understands the system
Understands the system
but, will test "gently"
but, will test "gently"
and, is driven by "delivery"
and, is driven by "delivery"
Must learn about the system,
Must learn about the system,
but, will attempt to break it
but, will attempt to break it
and, is driven by quality
and, is driven by quality

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Testing Strategy
System engineering
Analysis modeling
Design modeling
Code generation Unit test
Integration test
Validation test
System test

8
Testing Strategy
 We begin by ‘testing-in-the-small’ and move
toward ‘testing-in-the-large’
 For conventional software
 The module (component) is our initial focus
 Integration of modules follows
 For OO software
 our focus when “testing in the small” changes from
an individual module (the conventional view) to an
OO class that encompasses attributes and
operations and implies communication and
collaboration

9
Strategic Issues
 Specify product requirements in a quantifiable manner long
before testing commences.
 State testing objectives explicitly.
 Understand the users of the software and develop a profile
for each user category.
 Develop a testing plan that emphasizes “rapid cycle testin
g.”
 Build “robust” software that is designed to test itself (re-
route or cleanly terminate)
 Use effective technical reviews as a filter prior to testing
 Conduct technical reviews to assess the test strategy and
test cases themselves.
 Develop a continuous improvement approach for the testing
process.

10
Unit Testing
module
module
to be
to be
tested
tested
test cases
test cases
results
results
software
software
engineer
engineer

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Unit Testing
interface
interface
local data structures
boundary conditions
boundary conditions
independent paths
independent paths
error handling paths
module
module
to be
to be
tested
tested
test cases
test cases

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Unit Test Environment
Module
Module
stub
stub stub
stub
driver
driver
RESULTS
RESULTS
interface
interface
boundary conditions
boundary conditions
independent paths
independent paths
test cases
test cases

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Integration Testing Strategies
Options:
Options:
•
• the
the “
“big bang
big bang”
” approach (all at once)
approach (all at once)
•
• an incremental construction strategy
an incremental construction strategy

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Top Down Integration
top module is tested with
top module is tested with
stubs
stubs
stubs are replaced one at
stubs are replaced one at
a time, "depth first"
a time, "depth first"
as new modules are integrated,
as new modules are integrated,
some subset of tests is re-run
some subset of tests is re-run
A
A
B
B
C
C
D
D E
E
F
F G
G

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Bottom-Up Integration
drivers are replaced one at a
drivers are replaced one at a
time, "depth first"
time, "depth first"
worker modules are grouped into
worker modules are grouped into
builds and integrated
A
A
B
B
C
C
D
D E
E
F
F G
G
cluster
cluster

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Sandwich Testing
Top modules are
Top modules are
tested with stubs
tested with stubs
Worker modules are grouped into
Worker modules are grouped into
A
A
B
B
C
C
D
D E
E
F
F G
G
cluster
cluster

17
Regression Testing
 Regression testing is the re-execution of some subset of
tests that have already been conducted to ensure that
changes have not propagated unintended side effects
 Whenever software is corrected, some aspect of the
software configuration (the program, its documentation,
or the data that support it) is changed.
 Regression testing helps to ensure that changes (due to
testing or for other reasons) do not introduce
unintended behavior or additional errors.
 Regression testing may be conducted manually, by re-
executing a subset of all test cases or using automated
capture/playback tools.

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Smoke Testing
 A common approach for creating “daily builds” for product
software
 Smoke testing steps:
 Software components that have been translated into code are
integrated into a “build.”
• A build includes all data files, libraries, reusable modules, and engineered
components that are required to implement one or more product
functions.
 A series of tests is designed to expose errors that will keep the build
from properly performing its function.
• The intent should be to uncover “show stopper” errors that have the
highest likelihood of throwing the software project behind schedule.
 The build is integrated with other builds and the entire product (in its
current form) is smoke tested daily.
• The integration approach may be top down or bottom up.

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Object-Oriented Testing
 begins by evaluating the correctness and
consistency of the analysis and design models
 testing strategy changes
 the concept of the ‘unit’ broadens due to
encapsulation
 integration focuses on classes and their execution
across a ‘thread’ or in the context of a usage
scenario
 validation uses conventional black box methods
 test case design draws on conventional
methods, but also encompasses special
features

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OO Testing Strategy
 class testing is the equivalent of unit testing
 operations within the class are tested
 the state behavior of the class is examined
 integration applied three different strategies
 thread-based testing—integrates the set of
classes required to respond to one input or event
 use-based testing—integrates the set of classes
required to respond to one use case
 cluster testing—integrates the set of classes
required to demonstrate one collaboration

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WebApp Testing - I
 The content model for the WebApp is
reviewed to uncover errors.
 The interface model is reviewed to ensure that
all use cases can be accommodated.
 The design model for the WebApp is reviewed
to uncover navigation errors.
 The user interface is tested to uncover errors in
presentation and/or navigation mechanics.
 Each functional component is unit tested.

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WebApp Testing - II
 Navigation throughout the architecture is tested.
 The WebApp is implemented in a variety of different
environmental configurations and is tested for
compatibility with each configuration.
 Security tests are conducted in an attempt to exploit
vulnerabilities in the WebApp or within its
environment.
 Performance tests are conducted.
 The WebApp is tested by a controlled and monitored
population of end-users. The results of their interaction
with the system are evaluated for content and
navigation errors, usability concerns, compatibility
concerns, and WebApp reliability and performance.

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High Order Testing:
Complete System
 Validation testing
 Focus is on software requirements
 System testing
 Focus is on system integration
 Alpha/Beta testing
 Focus is on customer usage
 Recovery testing
 forces the software to fail in a variety of ways and verifies that recovery is properly
performed
 Security testing
 verifies that protection mechanisms built into a system will, in fact, protect it from
improper penetration
 Stress testing
 executes a system in a manner that demands resources in abnormal quantity,
frequency, or volume
 Performance Testing
 test the run-time performance of software within the context of an integrated system

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Debugging: A Diagnostic Process

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Debugging Effort
time required
time required
to diagnose the
to diagnose the
symptom and
symptom and
determine the
determine the
cause
cause
time required
time required
to correct the error
to correct the error
and conduct
and conduct
regression tests
regression tests

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Symptoms & Causes
symptom
symptom
cause
cause
symptom and cause may be
symptom and cause may be
geographically separated
geographically separated
symptom may disappear when
symptom may disappear when
another problem is fixed
another problem is fixed
cause may be due to a
cause may be due to a
combination of non-errors
combination of non-errors
cause may be due to a system
cause may be due to a system
or compiler error
or compiler error
cause may be due to
cause may be due to
assumptions that everyone
assumptions that everyone
believes
believes
symptom may be intermittent
symptom may be intermittent

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Consequences of Bugs
damage
mild
annoying
disturbing
serious
extreme
catastrophic
infectious
Bug Type
Bug Categories:
Bug Categories:
function-related bugs,
function-related bugs,system-related bugs, data bugs, coding bugs,
system-related bugs, data bugs, coding bugs,
design bugs, documentation bugs, standards
design bugs, documentation bugs, standards
violations, etc.
violations, etc.

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Debugging Techniques
brute force / testing
backtracking
induction
deduction

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Correcting the Error
 Is the cause of the bug reproduced in another part of the program? In
many situations, a program defect is caused by an erroneous
pattern of logic that may be reproduced elsewhere.
 What "next bug" might be introduced by the fix I'm about to make?
Before the correction is made, the source code (or, better, the
design) should be evaluated to assess coupling of logic and
data structures.
 What could we have done to prevent this bug in the first place? This
question is the first step toward establishing a statistical
software quality assurance approach. If you correct the process
as well as the product, the bug will be removed from the
current program and may be eliminated from all future
programs.

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Final Thoughts
 Think -- before you act to correct
 Use tools to gain additional insight
 If you’re at an impasse, get help from someone
else
 Once you correct the bug, use regression
testing to uncover any side effects

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