Quality Analyst Training - Gain America

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Verification and validation should establish
confidence that the software is fit for purpose
This does NOT mean completely free of
defects
Rather, it must be good enough for its
intended use and the type of use will
determine the degree of confidence that is
needed

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Verification: The software should conform
to its specification (Are we building the
product right?)
Validation: The software should do what
the user really requires (Are we building
the right product?)

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Requirements Phase
Specification Phase (Analysis)
Planning Phase
Design Phase
Implementation Phase
Integration and Testing
Maintenance
Retirement

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Is a whole life-cycle process - V & V
must be applied at each stage in the
software process.
Has two principal objectives
– The discovery of defects in a system
– The assessment of whether or not the
system is usable in an operational situation.

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Software inspections and walkthroughs
- Concerned with analysis of the static
system representation to discover
problems (static verification)
Software testing - Concerned with
exercising and observing product
behaviour (dynamic verification)

– The system is executed with test data and its
operational behaviour is observed

S t at ic
verifi cat io n

R equ irem ent s
s pecifi cat io n

P ro to ty pe

Hi g h-lev el
d es ig n

Fo rm al
s pecifi cat io n

Det ail ed
d es ig n

P rog ram

Dy nam i c
v ali dat io n

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Careful planning is required to get the most out of
testing and inspection processes
Planning should start early in the development
process
The plan should identify the balance between
static verification and testing
Test planning is about defining standards for the
testing process rather than describing product
tests

Requ ir em ent s
s pecifi cat io n

S y st em
s pecifi cat io n

S y st em
i nt eg rat io n
t es t pl an

Accep tan ce
t es t pl an

S ervi ce

Sy stem
d es ig n

Accep tan ce
t es t

Det ail ed
d es ig n

S u b-s ys tem
i nt eg rat io n
t es t pl an

Sy stem
i nt eg ratio n t est

S u b-s ys tem
i nt eg rat io n t est

M o du le an d
u ni t co de
and t ess

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The testing process
Requirements traceability
Tested items
Testing schedule
Test recording procedures
Hardware and software requirements
Constraints

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Informal examination of a product (document)
Made up of:
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developers
client
next phase developers
Software Quality Assurance group leader

Produces:
◦ list of items not understood
◦ list of items thought to be incorrect

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Involve people examining the source
representation with the aim of discovering
anomalies and defects
Do not require execution of a system so may be
used before implementation
May be applied to any representation of the
system (requirements, design, test data, etc.)
Very effective technique for discovering errors

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Many different defects may be discovered in
a single inspection. In testing, one defect
may mask another so several executions are
required
The reuse domain and programming
knowledge so reviewers are likely to have
seen the types of error that commonly arise

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Inspections and testing are complementary and
not opposing verification techniques
Both should be used during the V & V process
Inspections can check conformance with a
specification but not conformance with the
customer‟s real requirements
Inspections cannot check non-functional
characteristics such as performance, usability, etc.

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Formalised approach to document reviews
Intended explicitly for defect DETECTION
(not correction)
Defects may be logical errors, anomalies in
the code that might indicate an erroneous
condition (e.g. an un-initialised variable) or
non-compliance with standards

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A precise specification must be available
Team members must be familiar with the
organisation standards
Syntactically correct code must be available
An error checklist should be prepared
Management must accept that inspection will
increase costs early in the software process
Management must not use inspections for staff
appraisal

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System overview presented to inspection team
Code and associated documents are
distributed to inspection team in advance
Inspection takes place and discovered errors
are noted
Modifications are made to repair discovered
errors
Re-inspection may or may not be required

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Made up of at least 4 members
Author of the code being inspected
Inspector who finds errors, omissions and
inconsistencies
Reader who reads the code to the team
Moderator who chairs the meeting and notes
discovered errors
Other roles are Scribe and Chief moderator

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Checklist of common errors should be used to
drive the inspection
Error checklist is programming language
dependent
The 'weaker' the type checking, the larger the
checklist
Examples: Initialization, Constant naming, loop
termination, array bounds, etc.

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500 statements/hour during overview
125 source statement/hour during individual
preparation
90-125 statements/hour can be inspected
Inspection is therefore an expensive process
Inspecting 500 lines costs about 40 man/hours
effort (@ $50/hr = $2000!!!)

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Can reveal the presence of errors NOT their
absence
A successful test is a test which discovers one or
more errors
The only validation technique for non-functional
requirements
Should be used in conjunction with static
verification to provide full V&V coverage

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“Program testing can be a very effective way to
show the presents of bugs but is hopelessly
inadequate for showing their absence” [Dijkstra]
Fault: “bug” incorrect piece of code
Failure: result of a fault
Error: mistake made by the programmer/developer

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Defect testing and debugging are distinct
processes
Verification and validation is concerned with
establishing the existence of defects in a program
Debugging is concerned with locating and
repairing these errors
Debugging involves formulating a hypothesis
about program behaviour then testing these
hypotheses to find the system error

Test
resu lt s

Lo cat e
erro r

Test
cases

Sp eci ficat io n

Des ig n
erro r repai r

Repai r
erro r

R e-tes t
p rog ram

C o m po nent
t es ti ng

Int egrat io n
t es ti ng

So ftw are dev elo per

Ind epen den t tes ti ng team

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Component testing
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Testing of individual program components
Usually the responsibility of the component
developer (except sometimes for critical systems)
Tests are derived from the developer‟s experience

Integration testing
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Testing of groups of components integrated to
create a system or sub-system
The responsibility of an independent testing team
Tests are based on a system specification

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Only exhaustive testing can show a program is
free from defects. However, exhaustive testing is
impossible
Tests should exercise a system's capabilities
rather than its components
Testing old capabilities is more important than
testing new capabilities
Testing typical situations is more important than
boundary value cases

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Test data Inputs which have been devised

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Test cases Inputs to test the system and

to test the system

the predicted outputs from these inputs if
the system operates according to its
specification

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Test cases and test scenarios comprise
much of a software systems testware.
Black box test cases are developed by
domain analysis and examination of the
system requirements and specification.

Glass box test cases are developed by
examining the behavior of the source code.

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Test to specification:
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Black box,
Data driven
Functional testing
Code is ignored: only use specification document
to develop test cases

Test to code:
◦ Glass box/White box
◦ Logic driven testing
◦ Ignore specification and only examine the code.

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An approach to testing where the program
is considered as a „black-box‟
The program test cases are based on the
system specification
Test planning can begin early in the
software process

I

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Inp ut t est dat a

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Ou t pu t t est resu lt s

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Sometime called structural testing or glass-box
testing
Derivation of test cases according to program
structure
Knowledge of the program is used to identify
additional test cases
Objective is to exercise all program statements
(not all path combinations)

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Statement coverage ◦ Test cases which will execute every statement at least once.
◦ Tools exist for help
◦ No guarantee that all branches are properly tested. Loop
exit?

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Branch coverage
◦ All branches are tested once

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Path coverage - Restriction of type of paths:
◦ Linear code sequences
◦ Definition/Use checking (all definition/use paths)
◦ Can locate dead code

Test d at a

Test s

Deri ves

C o m po nent
cod e

Test
o ut pu ts

Quality Analyst Training - Gain America

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