Software Engineering, Lectures

1. SE-381
Software Engineering
BEIT-V
Lecture # 28
Testing (1 of 2)

2. Testing Principles
[Sch96] Ch – 5
• Purpose of Testing
– To detect faults – as many as possible
and as early as possible
– Correction of faults at early stages is
cheaper
– To produce high quality Software
• Testing as an Independent stage!
• Testing Integrated to each phase of
SDLC and Acceptance Testing of the
final product

3. Testing Intro (Contd.)
• Verification & Validation
– Verification refers to the process of determining
whether a phase has been correctly carried out,
and it takes place at the end of each phase
– Validation is the intensive evaluation process
that takes place just before the product is
delivered to the client – to determine whether the
product as a whole satisfies its Specifications
» Conforms to IEEE Software Engineering Glossary,
IEEE 610.12, 1990

4. Verification & Validation
• Barry Boehm 1984
– Verification: Are we building the Product Right?
– Validation: Are we building the Right Product?
– The former concentrates on the process and
later on the product.
– V & V and Testing are used alternatively by
different texts, but Schach uses Testing with
broader meanings encompassing Process as
well as Product

5. Types of Testing
Non-Execution Based
Testing
– Applicable to earlier
phases as well as
Coding phase
– Mostly comprised of
Walkthroughs and
Inspections of
Documents, Design
and Code
Execution Based
Testing
– Corresponds to the
phases when code is
available
– Applicable to
Implementation,
Integration and
Maintenance phases

6. Software Quality Assurance
• In Engineering Disciplines
– Quality is “Adherence to Specifications”
• Accordingly, the Quality of Software is
– the extent to which the product satisfies the
Specifications
– Its achievement needs ‘Effort’ and
‘Mechanism’
– SQA group should be amongst the ‘Strongest
groups’ in the Software Development setup
like Quality Control Department in Industry

7. SQA Group
• MUST ensure
– Correct Product is produced
– Product has been produced by following the
right process.
– At the end of each phase group should verify
that the produced deliverables conform to the
previous and next stage requirements
– That Software Process and organizations
capability to produce quality software is
improving

8. SQA Group (Contd)
– Should comprise of skilled, technical, Senior
members with expertise in varied areas of SD
– Number of its members should be proportional
to the scope and amount of SD undertaken by
the setup
– For small setups of <4 developers separate
group will be an overhead, so the individuals
should ensure SQA of parts developed /
authored by others
– Separate SQA Group costs but brings in more
benefits (in terms of repute and more work)
resulting from the delivery of High Quality
Software

9. SQA Group (Contd.)
• Managerial Independence
– The group should directly report to
CE/CEO of the setup
– Since it’ll have to make important, as well
as seemingly ‘detrimental’ decisions eg
“Buggy in-Time delivery” or “Bug-free (or
less buggy) delayed delivery”, and resolve
‘Conflicts of Interest’ among different
groups, so SQA Group should have
Managerial Independence

10. Non-Execution Based Testing
– Mostly comprised of document(s), Design and
Code reviews, and can be conducted through
– Should be done by a Team consisting of
members, most of whom were not involved in
the respective phase development
– Reviewing should be done independently by the
team members, with intention to find ‘Max
Faults’
– Can be carried out in two ways:
• Walkthroughs
• Inspections or Technical / Formal Reviews

11. Inspections Versus
Walkthroughs
Inspections
• More formal
• Checklists guide the
reviewers
• 5-step Method
• Takes longer then
WT
• More powerful and
cost-effective tool
Walkthroughs
• Informal
• 2-step method with
– Preparations
– Team Analysis of the
document

12. Walkthroughs
• Walkthrough team should be of 4-6
members including
• Representative from the developers involved in
respective (to be reviewed) phase
• Manager from the phase under review
• Representative from the Next phase – who have to use
this deliverable
• Representative from SQA Group (Chair)
• Representative from Client
– Professionally experienced can find important
faults
– Senior members more effective

13. Managing Walkthroughs
• The documents/material should be
circulated in advance
• Each reviewer, after detailed study, should
prepare two lists of:
1. Possible Faults
2. Items in-comprehensible (unclear)
• Aim is to ‘detect and record’ the faults not
to ‘correct’ them
• Walkthrough meetings be called and
chaired by SQA group member and should
not last more than two hours

14. Managing Walkthroughs .
• The Phase (one under review)
Representative guides the members to
walkthrough the document, this can be either
– Participant-Driven
• The prepared lists (1 & 2) are presented
• The Phase Rep should respond, justify or clarify each
item
• After reply, each item graded as ‘Fault’ or ‘Reviewers
Mistake’
– Document-Driven
• Phase Rep walks the participants through the document
• Reviewers interrupt by picking up from their own
prepared lists, or triggered by others response or
presentation

15. Managing Walkthroughs ..
• Document Driven approach
– Widely used,
– Applicable to Specification, Design, Plan and
Code Walkthroughs
– Prompts more faults
» IEEE Standards for Software Reviews IEEE 1028,
1988
• Performance at Walkthroughs should NOT
be used as ‘Evaluation’ of Team Members
• Walkthrough meetings should not turn into
‘Point-Scoring’ sessions – otherwise these
will forfeit the aim of Fault finding

16. Inspections
(or Reviews w.r.t [Jal05])
• Proposed by Fagan 1976 for testing of
Design and Code
– A more formal approach
– Comprised of 5 steps
• Overview – of the document/material by Phase Rep,
and after review it’ll be distributed among reviewers
• Preparation – Reviewers list the faults, aided by
provided Checklist, and remark their frequency, type etc
• Inspection – One Reviewer walks through the material
with reviewers ensuring every item is covered. All
identified faults be compiled by the Inspection Team
leader within the day
• Rework – Phase Rep should resolve all the faults,
problems and document their solutions

17. Inspections or Reviews (Contd.)
• Follow-up – The Team Leader to ensure that every
single item raised is satisfactorily resolved either by
fixing the document or clarifying the item.
– If more than 5% of the material inspected is
Reworked then team meets again for 100% re-
inspection
– Inspection Team should have at least 4
members – Moderator/Leader from SQAG,
Phase Rep, Next Phase Rep, Clients Rep
– Team members should take different roles of
Reader, Recorder, Moderator etc

18. CHECKLIST FOR HIGH LEVEL OR FUNCTION-ORIENTED DESIGN
Sr. # Items Yes/No
1. Is each of the functional requirements taken into account?
2. Are there analyses to demonstrate that performance requirements can be
met?
3. Are all assumptions explicitly stated, and are they acceptable?
4. Are there any limitations or constraints on the design beyond those in the
requirements?
5. Are external specifications of each module completely specified?
6. Have exceptional conditions been handled?
7. Are all the data formats consistent with the requirements?
8. Are the operator and user interfaces properly addressed?
9. Is the design modular, and does it conform to local standards?
10. Are the sizes of data structures estimated?
11. Are provisions made to guard against overflow?

19. CHECKLIST FOR DETAILED DESIGN
Sr.
#
Items Yes/No
1. Does each of the modules in the system design exist in
detailed design?
2. Are there analyses to demonstrate that the performance
requirements can be met?
3. Are all the assumptions explicitly stated, and are they
acceptable?
4. Are all relevant aspects of system design reflected in detailed
design?
5. Have the exceptional conditions been handled?
6. Are all the data formats consistent with the system design?
7. Is the design structured, and does it conform to local
standards?
8. Are the sizes of data structures estimated?

20. 9. Are provisions made to guard against overflow?
10. Is each statement specified in natural language easily
codable?
11. Are the loop termination conditions properly specified?
12. Are the conditions in the loops OK?
13. Are the conditions in the if statements correct?
14. Is the nesting proper?
15. Is the module logic too complex?
16. Are the modules highly cohesive?
CHECKLIST FOR DETAILED DESIGN (Cont.)
Sr.
#
Items Yes/No

21. Inspections Benefits
• Fault Statistics recorded add to historical
data and can identify the gray areas in SD
and weaknesses in organization
• 70-80% of all faults can be detected using
inspections before Module Testing is started
• 40% less faults were detected in the final
product when used Inspections rather than
Walkthroughs
» Fagan 1976
• Programmers productivity is increased and
resources needed are reduced by 25%
despite Inspection teams overhead

22. Inspection Metrics
• Metrics are to measure, monitor and
ultimately to control a process, and here to
show effectiveness of the Inspection process
– Fault Density – is number of faults per page of
Specifications, Design Document or per KLOC
(1000 lines of Code) of Code inspected
– Fault Severity – further categorization of faults
into Major (which lead to program failure or
crash) or Minor (which are not Major) faults per
unit material (page or KLOC)
– Fault Detection Efficiency – number of Major or
Minor faults detected per person-hour
– Fault Detection Rate – number of Major/Minor
faults detected per hour

23. Execution Based Testing
• Testing is to demonstrate the presence of
faults/bugs or errors
• A Successful Test case is (like the ‘Test’ in
Medical terminology) the one which locates
or identifies a bug in the product
“Program Testing can be very effective way
to show the presence of bugs, but it is
hopelessly inadequate for showing their
absence”
[Prof Dijkstra 1972]

24. That is, if a product is executed with Test
Data and the output is WRONG then the
Product definitely contains a Fault, but if the
output is CORRECT, then the product still
may contain a fault.
Faults are same as ‘bugs’ and can relate to
any phase of SDLC
Errors are usually programmer introduced
faults
Failure is an unacceptable effect or behavior,
under permissible operating conditions that
occur as a consequence of a fault.

25. What Should be Tested?
• Execution Based Testing is a process of
inferring certain behavioral properties of a
product based, in part, on the results of
executing the product in a known
environment with selected inputs
[Goodenough 1979]
– Three Key elements
• Inferential Process
• Known Environment(s)
• Selected Input(s)

26. Inferential Process
• Testing is an Inferential Process – the
product is run with known inputs
expecting a desired output.
• Tester has to infer, what if anything is
wrong with the product.
• Tester has Test Cases, Bug reports,
Code and its .exe with him and has to
identify the fault(s)

27. Known Environment(s)
• The Environment consists of Hardware,
OSs, Compilers and all other programs with
which the Product is to coexist and interact
with or to execute in their presence
• The Environment specifically refers to the
state of these components when a fault
occurred
• The faults (usually assigned) to the Product
may not be due to the Product but produced
by any other component of the environment
which is running at that time.

28. – These may satisfy the Input specifications but
may not produce the desired output
– In Real-Time (RT) systems, the exact inputs
may not be easy to feed to a specific Product, as
it will be one of the components of the system,
whose input will be the output of some other
component and may involve different A-D/D-A
conversions.
– For RT systems’ testing Simulators are used
and they provide the needed environment in
which the system is to run and hence the Input
data. Yet this will be a ‘simulated’ environment
different than the one in which Product has to
operate
Selected Input(s)

29. Testing - Behavioral
Properties
• Testing is to confirm that whether Product
functions correctly with respect to its
behavioral properties, which are
– Utility
– Reliability
– Robustness
– Performance and
– Correctness
[Goodenough 1979]
That is for these Behavioral Properties we test the Product.

30. Utility
Utility is the extent to which Users’ needs
are met when a correct Product is used
under conditions written by its
Specifications
Here we test for
• Ease of Use i.e. User friendliness
• Functionality – whether Product performs what
was desired
• Cost-effectiveness – otherwise it will not be
purchased, so it ought to be rightly/affordably
priced

31. Reliability
Reliability is the measure of the frequency and
criticality of Product failure
We use different metrics to measure Reliability,
these are:
• Mean time between failures – how often the product
fails
• Failure Severity – how ‘hard’ the effects of that failure
can be
• Mean time to Repair – how long it takes on average to
repair, more important is how long it takes to correct the
results of the failure. Eg crash (or failure) of email
browser might delete all the emails in ‘Inbox’ folder, or
can damage the ‘Address Book’, or a Db front-end
might wipe out the database on which it was operating.
So the repair of Product will include the correction of
allied problems and would surely take much longer.

32. Robustness
Robustness is the response from the Product
for any input, this response needs to be
reasonable and meaningful. It is essentially
a function of number of factors; range of
Operating conditions, unacceptable results
for valid input and acceptability of results for
invalid input.
• A Robust Product should
– NOT yield unacceptable results when the input satisfies
its specifications
– NOT crash when the Product is given invalid input
– Respond/guide the user for invalid input, eg &$*?
Characters used for string command, say while reading a
filename

33. Performance
Performance is the extent to which Product meets
its constraints with respect to response time or
space requirements. Embedded systems, used
in Industry, Avionics, PDA, Palmtop devices,
Mobiles etc have their own storage, size,
compute power constraints.
Here we test Product according to the application
domain
• RT systems need to perform within a response time range,
otherwise the produced results would be useless.
• Size/display constraints may lead to smaller storage/memory
sizes and minimal instruction sets, so the product need to be
developed within those constraints
• Critical information needs to be received and processed in
RT.

34. Correctness
Correctness is the extent of
conformance of the product to the
specifications, independent of its use of
computing resources, when operated
under permitted conditions.
[Goodenough 1979]
• Simply, if product is provided all resources it
needs, then for given valid input, it should
provide the valid output i.e. according to output
specifications

35. Formal Mathematical Proofs
• To prove that program is correct wrt its specification
are expensive to develop, so used in
Safety/Security and Life critical systems
• They use the knowledge of formal semantics of the
programming languages and construct theories that
relate the program with its formal specs
• These theories are proven mathematically, often
using complex theorem-proving programs
• They need specialist skills and have very high cost
• The proven correct also needs to be tested and
verified. {Sommerville, SE 6th Ed, 2000;p436)

36. Fault Handling Techniques
Testing
Fault Handling
Fault Avoidance
Fault Tolerance
Fault Detection
Debugging
Component
Testing
Integration
Testing
System
Testing
Verification
Configuration
Management
Atomic
Transactions
Modular
Redundancy
Correctness
Debugging
Performance
Debugging
Reviews
Design
Methodology

37. Reference for This Lecture
• Pankaj Jalote, (2004 / 2005), An Integrated
Approach to Software Engineering, 2nd / 3rd
Edition; Narosa Publishing House, New Delhi –
Chapter 5 / 10 – Testing pp: 403-471/409-471
• Stephen R Schach (1996); Classical and
Object Oriented Software Engineering; 3rd Ed,
Irwin-McGraw Hill, Boston, Ch-5 Testing
Principles; pp:109-138
• Rajib Mall (2005); Fundamentals of Software
Engineering, 2nd Ed, Prentice-Hall of India,
New Delhi; Ch-10 Coding and Testing, pp:248-
279