Software Testing (Contd..) SDLC Model

Software Engineering
Dr. Kamal Gulati
(Part 7) – Software Testing (Contd..)

Defect testing
 Testing programs to
establish the presence of
system defects

Objectives
 To understand testing techniques that are
geared to discover program faults
 To introduce guidelines for interface testing
 To understand specific approaches to object-
oriented testing
 To understand the principles of CASE tool
support for testing

Topics covered
 Defect testing
 Integration testing
 Object-oriented testing
 Testing workbenches

The testing process
 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

Testing phases
Component
testing
Integration
testing
Software developer Independent testing team

Defect testing
 The goal of defect testing is to discover defects
in programs
 A successful defect test is a test which causes a
program to behave in an anomalous way
 Tests show the presence not the absence of
defects

 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

The defect testing process
Design test
cases
Prepare test
data
Runprogram
withtest data
Compare results
totest cases
Test
cases
Test
data
Test
results
Test
reports

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
Input test data
OeOutput test results
System
Inputs causing
anomalous
behaviour
Outputs which reveal
the presence of
defects

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

System
Outputs
Invalid inputs Valid inputs

 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

Equivalence partitions
Between 10000 and 99999Less than 10000 More than 99999
9999
10000 50000
100000
99999
Input values
Between 4 and 10Less than 4 More than 10
3
4 7
11
10
Number of input values

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

 Sometime called white-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)
Structural testing

White-box testing
Component
code
Test
outputs
Test data
DerivesTests

Binary search (Java)
class BinSearch {
// This is an encapsulation of a binary search function that takes an array of
// ordered objects and a key and returns an object with 2 attributes namely
// index - the value of the array index
// found - a boolean indicating whether or not the key is in the array
// An object is returned because it is not possible in Java to pass basic types by
// reference to a function and so return two values
// the key is -1 if the element is not found
public static void search ( int key, int [] elemArray, Result r )
{
int bottom = 0 ;
int top = elemArray.length - 1 ;
int mid ;
r.found = false ; r.index = -1 ;
while ( bottom <= top )
{
mid = (top + bottom) / 2 ;
if (elemArray [mid] == key)
{
r.index = mid ;
r.found = true ;
return ;
} // if part
else
{
if (elemArray [mid] < key)
bottom = mid + 1 ;
else
top = mid - 1 ;
}
} //while loop
} // search
} //BinSearch

 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 - equiv. partitions

Binary search equiv. partitions
Mid-point
Elements < Mid Elements > Mid
Equivalence class boundaries

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

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

 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

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

Answer:
1. Object-Oriented Systems – because these have a neat
decomposition into classes and methods –makes testing
easy
2. Real-Time Systems – because we can identify slow bits of
code more quickly
3. systems with strict performance requirements – because we
can measure the performance of individual methods early in
the testing process
Q: For which types of system is bottom-up testing appropriate,
and why?

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

Testing approaches
 Architectural validation
• Top-down integration testing is better at discovering errors in
the system architecture
 System demonstration
• Top-down integration testing allows a limited demonstration at
an early stage in the development
 Test implementation
• Often easier with bottom-up integration testing
 Test observation
• Problems with both approaches. Extra code may be required
to observe tests

 Takes place when modules or sub-systems are
integrated to create larger systems
 Objectives are to detect faults due to interface
errors or invalid assumptions about interfaces
 Particularly important for object-oriented
development as objects are defined by their
interfaces
Interface testing

Interface testing
Test
cases
BA
C

Interfaces types
 Parameter interfaces
• Data passed from one procedure to another
 Shared memory interfaces
• Block of memory is shared between procedures
 Procedural interfaces
• Sub-system encapsulates a set of procedures to be called by
other sub-systems
 Message passing interfaces
• Sub-systems request services from other sub-systems

Interface errors
 Interface misuse
• A calling component calls another component and makes an
error in its use of its interface e.g. parameters in the wrong
order
 Interface misunderstanding
• A calling component embeds assumptions about the
behaviour of the called component which are incorrect
 Timing errors
• The called and the calling component operate at different
speeds and out-of-date information is accessed

Interface testing guidelines
 Design tests so that parameters to a called
procedure are at the extreme ends of their
ranges
 Always test pointer parameters with null
pointers
 Design tests which cause the component to fail
 Use stress testing in message passing systems
 In shared memory systems, vary the order in
which components are activated

Stress testing
 Exercises the system beyond its maximum
design load. Stressing the system often causes
defects to
come to light
 Stressing the system test failure behaviour..
Systems should not fail catastrophically. Stress
testing checks for unacceptable loss of service
or data
 Particularly relevant to distributed systems
which can exhibit severe degradation as a
network becomes overloaded

 The components to be tested are object classes
that are instantiated as objects
 Larger grain than individual functions so
approaches to white-box testing have to be
extended
 No obvious ‘top’ to the system for top-down
integration and testing
Object-oriented testing

Testing levels
 Testing operations associated with objects
 Testing object classes
 Testing clusters of cooperating objects
 Testing the complete OO system

Object class testing
 Complete test coverage of a class involves
• Testing all operations associated with an object
• Setting and interrogating all object attributes
• Exercising the object in all possible states
 Inheritance makes it more difficult to design
object class tests as the information to be tested
is not localised

Weather station object interface
 Test cases are needed for
all operations
 Use a state model to
identify state transitions for
testing
 Examples of testing
sequences
• Shutdown  Waiting  Shutdown
• Waiting  Calibrating  Testing 
Transmitting  Waiting
• Waiting  Collecting  Waiting 
Summarising  Transmitting  Waiting
identifier
reportWeather ()
calibrate (instruments)
test ()
startup (instruments)
shutdown (instruments)
WeatherStation

Object integration
 Levels of integration are less distinct in object-
oriented systems
 Cluster testing is concerned with integrating and
testing clusters of cooperating objects
 Identify clusters using knowledge of the
operation of objects and the system features
that are implemented by these clusters

Approaches to cluster testing
 Use-case or scenario testing
• Testing is based on a user interactions with the system
• Has the advantage that it tests system features as
experienced by users
 Thread testing
• Tests the systems response to events as processing threads
through the system
 Object interaction testing
• Tests sequences of object interactions that stop when an
object operation does not call on services from another object

Scenario-based testing
 Identify scenarios from use-cases and
supplement these with interaction diagrams that
show the objects involved in the scenario
 Consider the scenario in the weather station
system where a report is generated

Weather station testing
 Thread of methods executed
• CommsController:request  WeatherStation:report 
WeatherData:summarise
 Inputs and outputs
• Input of report request with associated acknowledge and a
final output of a report
• Can be tested by creating raw data and ensuring that it is
summarised properly
• Use the same raw data to test the WeatherData object

Testing workbenches
 Testing is an expensive process phase. Testing
workbenches provide a range of tools to reduce
the time required and total testing costs
 Most testing workbenches are open systems
because testing needs are organisation-specific
 Difficult to integrate with closed design and
analysis workbenches

Testing workbench adaptation
 Scripts may be developed for user interface
simulators and patterns for test data generators
 Test outputs may have to be prepared manually
for comparison
 Special-purpose file comparators may be
developed

Key points
 Test parts of a system which are commonly used
rather than those which are rarely executed
 Equivalence partitions are sets of test cases
where the program should behave in an
equivalent way
 Black-box testing is based on the system
specification
 Structural testing identifies test cases which
cause all paths through the program to be
executed

Key points
 Test coverage measures ensure that all
statements have been executed at least
once.
 Interface defects arise because of
specification misreading, misunderstanding,
errors or invalid timing assumptions
 To test object classes, test all operations,
attributes and states
 Integrate object-oriented systems around
clusters of objects

ThankYou&
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