Software testing-and-analysis

Ultimate goal for software testing
Quality
Assurance

V & V goals
• 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

• 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?)
Verification vs. validation

“Classical” lifecycle model
• Requirements Phase
• Specification Phase (Analysis)
• Planning Phase
• Design Phase
• Implementation Phase
• Integration and Testing
• Maintenance
• Retirement

Cost to fix faults
Cost
Definition Development Post Release
1*
1.5* to 6*
60* to 100*

• 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.
The V & V process

Sequential model
Requireme
nts
Testing/Ver
ify
Integration
Testing/Ver
ify
Operations
Mode
Specificatio
n
Testing/Ver
ify
Planning
Testing/Ver
ifyDesign
Testing/Ver
ifyImplementa
tion
Testing/Veri
fy
Maintenance

• 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
Static and dynamic verification

Static and dynamic V&V
Formal
specification
High-level
design
Requirements
specification
Detailed
design
Program
Prototype
Dynamic
validation
Static
verification

• 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
V & V planning

The V-model of development
Requirements
specification
System
specification
System
design
Detailed
design
Moduleand
unitcode
and tess
Sub-system
integration
test plan
System
integration
test plan
Acceptance
test plan
Service
Acceptance
test
System
integrationtest
Sub-system
integrationtest

The structure of a software test plan
• The testing process
• Requirements traceability
• Tested items
• Testing schedule
• Test recording procedures
• Hardware and software requirements
• Constraints

Walkthroughs
• Informal examination of a product (document)
• Made up of:
– developers
– client
– next phase developers
– Software Quality Assurance group leader
• Produces:
– list of items not understood
– list of items thought to be incorrect

Software inspections
• 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

Inspection success
• 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

Inspections and testing
• 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.

Program inspections
• 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

Inspection pre-conditions
• 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

Inspection procedure
• 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

Inspection teams
• 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

Inspection checklists
• 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.

Inspection rate
• 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!!!)

• 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
Program testing

Execution based testing
• “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

• 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
Testing and debugging

The debugging process
Locate
error
Design
errorrepair
Repair
error
Re-test
program
Test
results Specification Test
cases

Testing phases
Component
testing
Integration
testing
Software developer Independent testingteam

Testing phases
• Component testing
– 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
– 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

• 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
Testing priorities

• Test data Inputs which have been
devised to test the system
• Test cases Inputs to test the system and
the predicted outputs from these inputs if
the system operates according to its
specification
Test data and test cases

Development of test cases
• 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.

The defect testing process
Design test
cases
Prepare test
data
Run program
with test data
Compare results
to test cases
Test
cases
Test
data
Test
results
Test
reports

Methods of testing
• Test to specification:
– 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.

Can you guarantee a program is
correct?
• This is called the Halting Problem
• Write a program to test if any given program
is correct. The output is correct or incorrect.
• Test this program on itself.
• If output is incorrect, then how do you know
the output is correct?
• Conundrum, Dilemma, or Contradiction?

Black-box testing
• 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

Black-box testing
I
e
Inputtestdata
OeOutputtestresults
System
Inputscausing
anomalous
behaviour
Outputswhichreveal
thepresenceof
defects

Pairing down test cases
• Use methods that take advantage of
symmetries, data equivalencies, and
independencies to reduce the number of
necessary test cases.
– Equivalence Testing
– Boundary Value Analysis
• Determine the ranges of working system
• Develop equivalence classes of test cases
• Examine the boundaries of these classes
carefully

Equivalence partitioning
• Input data and output results often fall
into different classes where all members
of a class are related
• Each of these classes is an equivalence
partition where the program behaves in
an equivalent way for each class member
• Test cases should be chosen from each
partition

Equivalence partitioning
System
Outputs
Invalidinputs Validinputs

• Partition system inputs and outputs into
‘equivalence sets’
– If input is a 5-digit integer between 10,000 and
99,999, equivalence partitions are < 10,000,
10,000 - 99, 999 and > 10, 000
• Choose test cases at the boundary of these
sets
– 00000, 09999, 10000, 99999, 10001
Boundary value testing

Equivalence partitions
Between10000and99999Lessthan10000 Morethan99999
9999
10000 50000
100000
99999
Inputvalues
Between4and10Lessthan4 Morethan10
3
4 7
11
10
Numberofinputvalues

Search routine specification
procedure Search (Key : ELEM ; T: ELEM_ARRAY;
Found : in out BOOLEAN; L: in out ELEM_INDEX) ;
Pre-condition
-- the array has at least one element
T’FIRST <= T’LAST
Post-condition
-- the element is found and is referenced by L
( Found and T (L) = Key)
or
-- the element is not in the array
( not Found and
not (exists i, T’FIRST >= i <= T’LAST, T (i) = Key ))

• Inputs which conform to the pre-conditions
• Inputs where a pre-condition does not hold
• Inputs where the key element is a member of
the array
• Inputs where the key element is not a member
of the array
Search routine - input partitions

Testing guidelines - sequences
• Test software with sequences which have
only a single value
• Use sequences of different sizes in
different tests
• Derive tests so that the first, middle and
last elements of the sequence are
accessed
• Test with sequences of zero length

Search routine - input partitions
Array Element
Single value In sequence
Single value Not in sequence
More than 1 value First element in sequence
More than 1 value Last element in sequence
More than 1 value Middle element in sequence
More than 1 value Not in sequence
Input sequence (T) Key (Key) Output (Found, L)
17 17 true, 1
17 0 false, ??
17, 29, 21, 23 17 true, 1
41, 18, 9, 31, 30, 16, 45 45 true, 7
17, 18, 21, 23, 29, 41, 38 23 true, 4
21, 23, 29, 33, 38 25 false, ??

Sorting example
• Example: sort (lst, n)
– Sort a list of numbers
– The list is between 2 and 1000 elements
• Domains:
– The list has some item type (of little concern)
– n is an integer value (sub-range)
• Equivalence classes;
– n < 2
– n > 1000
– 2 <= n <= 1000

Sorting example
• What do you test?
• Not all cases of integers
• Not all cases of positive integers
• Not all cases between 1 and 1001
• Highest payoff for detecting faults is to test around
the boundaries of equivalence classes.
• Test n=1, n=2, n=1000, n=1001, and say n= 10
• Five tests versus 1000.

• 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)
White-box testing

Types of structural testing
• 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?
• Branch coverage
– All branches are tested once
• Path coverage - Restriction of type of paths:
– Linear code sequences
– Definition/Use checking (all definition/use paths)
– Can locate dead code

White-box testing
Component
code
Test
outputs
Test data
DerivesTests

White box testing - binary search example
int search ( int key, int [] elemArray)
{
int bottom = 0;
int top = elemArray.length - 1;
int mid;
int result = -1;
while ( bottom <= top )
{
mid = (top + bottom) / 2;
if (elemArray [mid] == key)
{
result = mid;
return result;
} // if part
else
{
if (elemArray [mid] < key)
bottom = mid + 1;
else
top = mid - 1;
}
} //while loop
return result;
} // search

• Pre-conditions satisfied, key element in array
• Pre-conditions satisfied, key element not in
array
• Pre-conditions unsatisfied, key element in
array
• Pre-conditions unsatisfied, key element not in
array
• Input array has a single value
• Input array has an even number of values
• Input array has an odd number of values
Binary search equivalence partitions

Binary search equivalence partitions
Mid-point
Elements<Mid Elements>Mid
Equivalenceclassboundaries

Binary search - test cases
Input array (T) Key (Key) Output (Found, L)
17 17 true, 1
17 0 false, ??
17, 21, 23, 29 17 true, 1
9, 16, 18, 30, 31, 41, 45 45 true, 7
17, 18, 21, 23, 29, 38, 41 23 true, 4
17, 18, 21, 23, 29, 33, 38 21 true, 3
12, 18, 21, 23, 32 23 true, 4
21, 23, 29, 33, 38 25 false, ??

Path testing
• The objective of path testing is to ensure that
the set of test cases is such that each path
through the program is executed at least once
• The starting point for path testing is a program
flow graph that shows nodes representing
program decisions and arcs representing the
flow of control
• Statements with conditions are therefore nodes
in the flow graph

• Describes the program control flow. Each
branch is shown as a separate path and loops
are shown by arrows looping back to the loop
condition node
• Used as a basis for computing the cyclomatic
complexity
• Cyclomatic complexity = Number of edges -
Number of nodes +2
Program flow graphs

• The number of tests to test all control
statements equals the cyclomatic complexity
• Cyclomatic complexity equals number of
conditions in a program
• Useful if used with care. Does not imply
adequacy of testing
• Although all paths are executed, all
combinations of paths are not executed
Cyclomatic complexity

1
2
3
4
65
7
while bottom <= top
if (elemArray [mid] == key
(if (elemArray [mid]< key8
9
bottom > top
Binary search flow
graph

• 1, 2, 3, 8, 9
• 1, 2, 3, 4, 6, 7, 2
• 1, 2, 3, 4, 5, 7, 2
• 1, 2, 3, 4, 6, 7, 2, 8, 9
• Test cases should be derived so that
all of these paths are executed
• A dynamic program analyser may be
used to check that paths have been
executed
Independent paths

Feasibility
• Pure black box testing (specification) is
realistically impossible because there are (in
general) too many test cases to consider.
• Pure testing to code requires a test of every
possible path in a flow chart. This is also (in
general) infeasible. Also every path does not
guarantee correctness.
• Normally, a combination of Black box and
Glass box testing is done.

Integration testing
• Tests complete systems or subsystems
composed of integrated components
• Integration testing should be black-box testing
with tests derived from the specification
• Main difficulty is localising errors
• Incremental integration testing reduces this
problem

Incremental integration testing
T3
T2
T1
T4
T5
A
B
C
D
T2
T1
T3
T4
A
B
C
T1
T2
T3
A
B
Test sequence
1
Test sequence
2
Test sequence
3

Approaches to integration testing
• Top-down testing
– Start with high-level system and integrate from the
top-down replacing individual components by stubs
where appropriate
• Bottom-up testing
– Integrate individual components in levels until the
complete system is created
• In practice, most integration involves a
combination of these strategies

Top-down testing
Level 2Level 2Level 2Level 2
Level 1 Level 1
Testing
sequence
Level 2
stubs
Level 3
stubs
. . .

Bottom-up testing
Level NLevel NLevel NLevel NLevel N
Level N–1 Level N–1Level N–1
Testing
sequence
Test
drivers
Test
drivers

Software testing metrics
• Defects rates
• Errors rates
• Number of errors
• Number of errors found per person hours
expended
• Measured by:
– individual
– module
– during development
• Errors should be categorized by origin, type,
cost

More metrics
• Direct measures - cost, effort, LOC, etc.
• Indirect Measures - functionality, quality,
complexity, reliability, maintainability
• Size Oriented:
– Lines of code - LOC
– Effort - person months
– errors/KLOC
– defects/KLOC
– cost/KLOC

Software testing-and-analysis

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