SOFTWARE QUALITY
ASSURANCE
LECTURE 02 : WEEK 02
SEN 460
: SPRING 2016
TEXT AND REF. BOOKS
Text Book:
Software Quality Engineering by Jeff Tian IEEE
Reference Book:
Software Quality Engineering A practitioners Approach IEEE
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sumeerahashmics/sqa
MS (Software Engineering)
BCIT(Ned University of Engineering and Technology) Email : [email protected]
Presented by: Sumeera Hashmi
SOFTWARE QUALITY
ASSURANCE ?
Failure, Error, Fault and
Defect
Failure
A failure is said to occur whenever the external behavior of a system
does not conform to that prescribed in the system specification.
Error
An error is a state of the system
An error state could lead to a failure in the absence of any corrective
action by the system.
Fault
A fault is the adjusted cause of an error.
Defect
Defect Prevention
Techniques?
Goal
To reduce the chance for defect injections
and the subsequent cost to deal with these
injected defects.
Assumption
There are known error sources or
Error sources
If
human misconception are the error
sources, education and training can help.
If
imprecise
designs
and
Error sources
If
certain tools or technologies can reduce
the
fault
injection
under
similar
environments they should be adopted.
Defect Prevention techniques
Education and Training
Education and Training provide people-based
solution, it can help software professionals to
improve, manage and control their work.
Formal Methods
Formal methods provide a way to eliminate certain
Education and Training
The education and training effort for error source
elimination should focus on following areas:
Product and Domain specific knowledge. If the people
involved are not familiar with the product type or
application domain there is a good chance that wrong solution will be implemented. E.g. developers
unfamiliar with the embedded software may design software with considering its environmental
Education and Training
Software development knowledge and expertise plays
an important role in developing high-quality software products. E.g. Lack of expertise with requirement analysis and product specification usually leads to many problems and rework in subsequent design, coding and testing.
Knowledge about development methodology, tools and
Formal methods
Development process knowledge. E.g. increment
Formal methods includes formal specifications
Defect Reduction
For most large systems in use today it is
unrealistic to expect the defect
prevention activities to be 100%
Inspection
Software inspections are critical examination of
software artifacts by human inspectors aimed at
discovering and fixing faults in the software system.
Inspection are critical reading and analysis of software code or other
software artifact
Inspections are typically conducted by multiple human inspectors,
through some coordination process.
Faults are detected directly by human inspectors.
Identified faults need to be removed as a results of the inspection
process and their removal also needs to be verified.
The formality of inspection vary from informal reviews and
Testing
Testing is one of the most important part of
QA. Testing involves the execution of
software and observation of the program
behavior.
If a failure is observed the execution record
Testing
Because testing is an execution based QA activity, a
pre-requisite to actual testing is the implemented software units, component, or system to be tested.
Actual testing can be divided into various sub phases
starting from the coding phase up-to the product release including:
Unit testing
Component testing
Integration testing
System Testing
Black Box and White Box
testing
Black Box or functional testing verifies the
correct handling of the external functions
provided by the software, or whether the
observed
behavior
conforms
to
user
expectation or product specification.
Black Box and White Box testing
When black-box testing is performed, failure related to specific external functions can be observed, leading to corresponding faults being detected and removed. The emphasis is on reducing the chances of encountering functional problems by target customers.
When or at what defect level to stop
Testing?
Most of the traditional testing techniques use
coverage information as the stopping criteria.
With the implicit assumption that higher the
coverage means higher quality or lower level
of defects.
Every statement or unit in a component must
be covered before subsequent integration
testing integration testing.
Other testing techniques include control flow
When or at what defect level to stop
Testing?
Domain testing that attempt to cover
boundaries between different input
sub-domains .
Product Reliability Goal
can be used as a
more objective criterion.
The testing is performed under an environment that
resembles actual usage by target customers so that
realistic reliability assessment can be obtained.
When or at what defect level to stop
Testing?
The coverage criterion ensures that certain
type of faults are detected and removed thus
reducing the number of defect to a lower level.
The usage base testing ensures that the faults
Defect Containment
Because of large software system in use
today, the defect reduction activities can
only reduce the number of faults to a
certain
level
But
not
completely
eliminate them.
This low level may still be inadequate for real
Fault tolerance
Software Fault tolerance ideas originate
from traditional hardware system
In such system spare parts or backup units are
commonly
used
to
keep
the
system
operational may be at low capability.
Fault tolerance
Recovery Blocks use repeated executions (or redundancy
over time) as the basic mechanism for fault tolerance. If dynamic failure in some local area is detected a portion of the latest execution is repeated therefore local failure will not propagate to global failure.
NVP uses parallel redundancy, where N-copies, each of a
Validation activities check whether a function need
and expected by the customer is present in the
software product. An absence of an expected function
is a deviation from expected behavior
Software verification activities check the conformance of a software system to its specification.
Failures involved in verification activities are internal failure,
e.g. how a component works with another component is a verification activity.
Validation activities
QA activities that can be classified as validation activities
System testing, where the focus is the overall set of
system functions to be provided to user
Acceptance testing and beta testing, where the focus is
assessment of software acceptance or performance by users
Usage-based statistical testing, where the operational
environment by target user is simulated during software testing before product release.
Software fault tolerance, which focuses on providing
Verification and Validation in V-Model
A variation of the waterfall model where each
development
phase
is
related
to
its
corresponding verification and validation activity.
Customer
requirements
are
validated
by
operational use.
Exsercise
Question 1
Black Box Testing (BBT) focuses on the functional requirements of the software. It enables the software engineer to derive sets of input
conditions that will fully exercise all functional requirements for a program. Suppose an SQA team is doing Black-Box testing of a
software. After testing the software the team reported that there are no errors in the software. But the project manager wants the same software to be tested using white box testing technique in order to eliminate all chances of errors. The Team started white box testing of the same software and uncovered errors which were not previously uncovered by the BBT.
Considering the above situation provide three examples of errors
Any Questions !!!
END OF LECTURE
