Chapter%207,%20Object%20Design

1
Chapter 7,Object Design
2
Object Design

• Object design is the process of adding details to
  the requirements analysis and making
  implementation decisions
• The object designer must choose among different
  ways to implement the analysis model with the
  goal to minimize execution time, memory and other
  measures of cost.
• Requirements Analysis Use cases, functional and
  dynamic model deliver operations for object model
• Object Design We iterate on where to put these
  operations in the object model
• Object Design serves as the basis of
  implementation

3
Object Design Closing the Gap
4
Object Design Issues

• Full definition of associations
• Full definition of classes
• Choice of algorithms and data structures
• Detection of new application-domain independent
  classes (example Cache)
• Optimization
• Increase of inheritance
• Decision on control
• Packaging

5
Terminology of Activities

• Object-Oriented Methodologies
• System Design
• Decomposition into subsystems
• Object Design
• Implementation language chosen
• Data structures and algorithms chosen
• SA/SD uses different terminology
• Preliminary Design
• Decomposition into subsystems
• Data structures are chosen
• Detailed Design
• Algorithms are chosen
• Data structures are refined
• Implementation language is chosen
• Typically in parallel with preliminary design,
  not separate stage

6
Object Design Activities

• 1. Service specification
• Describes precisely each class interface
• 2. Component selection
• Identify off-the-shelf components and additional
  solution objects
• 3. Object model restructuring
• Transforms the object design model to improve its
  understandability and extensibility
• 4. Object model optimization
• Transforms the object design model to address
  performance criteria such as response time or
  memory utilization.

7
Service Specification

• Requirements analysis
• Identifies attributes and operations without
  specifying their types or their parameters.
• Object design
• Add visibility information
• Add type signature information
• Add contracts

8
Add Visibility

• UML defines three levels of visibility
• Private
• A private attribute can be accessed only by the
  class in which it is defined.
• A private operation can be invoked only by the
  class in which it is defined.
• Private attributes and operations cannot be
  accessed by subclasses or other classes.
• Protected
• A protected attribute or operation can be
  accessed by the class in which it is defined and
  on any descendent of the class.
• Public
• A public attribute or operation can be accessed
  by any class.

9
Information Hiding Heuristics

• Build firewalls around classes
• Carefully define public interfaces for classes as
  well as subsystems
• Apply Need to know principle. The fewer an
  operation knows
• the less likely it will be affected by any
  changes
• the easier the class can be changed
• Trade-off
• Information hiding vs efficiency

10
Information Hiding Design Principles

• Only the operations of a class are allowed to
  manipulate its attributes
• Access attributes only via operations.
• Hide external objects at subsystem boundary
• Define abstract class interfaces which mediate
  between system and external world as well as
  between subsystems
• Do not apply an operation to the result of
  another operation.
• Write a new operation that combines the two
  operations.

11
Add Type Signature Information
Hashtable
-numElementsint
put()
get()
remove()
containsKey()
size()
12
Contracts

• Contracts on a class enable caller and callee to
  share the same assumptions about the class.
• Contracts include three types of constraints
• Invariant A predicate that is always true for
  all instances of a class. Invariants are
  constraints associated with classes or
  interfaces. Invariants are used to specify
  consistency constraints among class attributes.
• Precondition A predicate that must be true
  before an operation is invoked. Preconditions are
  associated with a specific operation.
  Preconditions are used to specify constraints
  that a caller must meet before calling an
  operation.
• Postcondition A predicate that must be true
  after an operation is invoked. Postconditions are
  associated with a specific operation.
  Postconditions are used to specify constraints
  that the object must ensure after the invocation
  of the operation.

13
Expressing constraints in UML

• OCL (Object Constraint Language)
• OCL allows constraints to be formally specified
  on single model elements or groups of model
  elements
• A constraint is expressed as an OCL expression
  returning the value true or false. OCL is not a
  procedural language (cannot constrain control
  flow).
• OCL expressions for Hashtable operation put()
• Invariant
• context Hashtable inv numElements gt 0
• Precondition
• context Hashtableput(key, entry)
  pre!containsKey(key)
• Post-condition
• context Hashtableput(key, entry) post
  containsKey(key) and get(key) entry

OCL expression
Context is a class operation
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Expressing Constraints in UML

• A constraint can also be depicted as a note
  attached to the constrained UML element by a
  dependency relationship.

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Object Design Areas

• 1. Service specification
• Describes precisely each class interface
• 2. Component selection
• Identify off-the-shelf components and additional
  solution objects
• 3. Object model restructuring
• Transforms the object design model to improve its
  understandability and extensibility
• 4. Object model optimization
• Transforms the object design model to address
  performance criteria such as response time or
  memory utilization.

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Component Selection

• Select existing off-the-shelf class libraries,
  frameworks or components
• Adjust the class libraries, framework or
  components
• Change the API if you have the source code.
• Use the adapter or bridge pattern if you dont
  have access

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Reuse...

• Look for existing classes in class libraries
• JSAPI, JTAPI, ....
• Select data structures appropriate to the
  algorithms
• Container classes
• Arrays, lists, queues, stacks, sets, trees, ...
• Define new internal classes and operations only
  if necessary
• Complex operations defined in terms of
  lower-level operations might need new classes and
  operations

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Object Design Areas

• 1. Service specification
• Describes precisely each class interface
• 2. Component selection
• Identify off-the-shelf components and additional
  solution objects
• 3. Object model restructuring
• Transforms the object design model to improve its
  understandability and extensibility
• 4. Object model optimization
• Transforms the object design model to address
  performance criteria such as response time or
  memory utilization.

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Restructuring Activities
This Lecture

• Realizing associations
• Revisiting inheritance to increase reuse
• Revising inheritance to remove implementation
  dependencies

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Increase Inheritance

• Rearrange and adjust classes and operations to
  prepare for inheritance
• Abstract common behavior out of groups of classes
• If a set of operations or attributes are repeated
  in 2 classes the classes might be special
  instances of a more general class.
• Be prepared to change a subsystem (collection of
  classes) into a superclass in an inheritance
  hierarchy.

21
Building a super class from several classes

• Prepare for inheritance. All operations must have
  the same signature but often the signatures do
  not match
• Some operations have fewer arguments than others
  Use overloading (Possible in Java)
• Similar attributes in the classes have different
  names Rename attribute and change all the
  operations.
• Operations defined in one class but no in the
  other Use virtual functions and class function
  overriding.
• Abstract out the common behavior (set of
  operations with same signature) and create a
  superclass out of it.
• Superclasses are desirable. They
• increase modularity, extensibility and
  reusability
• improve configuration management

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Implement Associations

• Strategy for implementing associations
• Be as uniform as possible
• Individual decision for each association
• Example of uniform implementation
• 1-to-1 association
• Role names are treated like attributes in the
  classes and translate to references
• 1-to-many association
• Translate to Vector
• Qualified association
• Translate to Hash table

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Unidirectional 1-to-1 Association
Object design model before transformation
MapArea
ZoomInAction
1
1
Object design model after transformation
MapArea
ZoomInAction
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Bidirectional 1-to-1 Association
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1-to-Many Association
Object design model before
transformation
Layer
LayerElement
1

Object design model after transformation
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Qualification
27
Object Design Areas

• 1. Service specification
• Describes precisely each class interface
• 2. Component selection
• Identify off-the-shelf components and additional
  solution objects
• 3. Object model restructuring
• Transforms the object design model to improve its
  understandability and extensibility
• 4. Object model optimization
• Transforms the object design model to address
  performance criteria such as response time or
  memory utilization.

28
Design Optimizations

• Design optimizations are an important part of the
  object design phase
• The requirements analysis model is semantically
  correct but often too inefficient if directly
  implemented.
• Optimization activities during object design
• 1. Add redundant associations to minimize access
  cost
• 2. Rearrange computations for greater efficiency
• 3. Store derived attributes to save computation
  time
• As an object designer you must strike a balance
  between efficiency and clarity.
• Optimizations will make your models more obscure

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Design Optimization Activities

• 1. Add redundant associations
• What are the most frequent operations? ( Sensor
  data lookup?)
• How often is the operation called? (30 times a
  month, every 50 milliseconds)
• 2. Rearrange execution order
• Eliminate dead paths as early as possible (Use
  knowledge of distributions, frequency of path
  traversals)
• Narrow search as soon as possible
• Check if execution order of loop should be
  reversed
• 3. Turn classes into attributes

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Implement Application domain classes

• To collapse or not collapse Attribute or
  association?
• Object design choices
• Implement entity as embedded attribute
• Implement entity as separate class with
  associations to other classes
• Associations are more flexible than attributes
  but often introduce unnecessary indirection.

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Optimization Activities Collapsing Objects
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To Collapse or not to Collapse?

• Collapse a class into an attribute if the only
  operations defined on the attributes are Set()
  and Get().

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Design Optimizations (continued)

• Store derived attributes
• Example Define new classes to store information
  locally (database cache)
• Problem with derived attributes
• Derived attributes must be updated when base
  values change.
• There are 3 ways to deal with the update
  problem
• Explicit code Implementor determines affected
  derived attributes (push)
• Periodic computation Recompute derived attribute
  occasionally (pull)
• Active value An attribute can designate set of
  dependent values which are automatically updated
  when active value is changed (notification, data
  trigger)

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Optimization Activities Delaying Complex
Computations
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Documenting the Object Design The Object Design
Document (ODD)

• Object design document
• Same as RAD ...
• additions to object, functional and dynamic
  models (from solution domain)
• Navigational map for object model
• Javadoc documentation for all classes
• ODD Management issues
• Update the RAD models in the RAD?
• Should the ODD be a separate document?
• Who is the target audience for these documents
  (Customer, developer?)
• If time is short Focus on the Navigational Map
  and Javadoc documentation?
• Example of acceptable ODD
• http//macbruegge1.informatik.tu-muenchen.de/james
  97/index.html

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Documenting Object Design ODD Conventions

• Each subsystem in a system provides a service
  (see Chapter on System Design)
• Describes the set of operations provided by the
  subsystem
• Specifying a service operation as
• Signature Name of operation, fully typed
  parameter list and return type
• Abstract Describes the operation
• Pre Precondition for calling the operation
• Post Postcondition describing important state
  after the execution of the operation
• Use JavaDoc for the specification of service
  operations.

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JavaDoc

• Add documentation comments to the source code.
• A doc comment consists of characters between /
  and /
• When JavaDoc parses a doc comment, leading
  characters on each line are discarded. First,
  blanks and tabs preceding the initial
  characters are also discarded.
• Doc comments may include HTML tags
• Example of a doc comment
• /
• This is a ltbgt doc lt/bgt comment
• /

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More on Java Doc

• Doc comments are only recognized when placed
  immediately before class, interface, constructor,
  method or field declarations.
• When you embed HTML tags within a doc comment,
  you should not use heading tags such as lth1gt and
  lth2gt, because JavaDoc creates an entire
  structured document and these structural tags
  interfere with the formatting of the generated
  document.
• Class and Interface Doc Tags
• Constructor and Method Doc Tags

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Class and Interface Doc Tags

• _at_author name-text
• Creates an Author entry.
• _at_version version-text
• Creates a Version entry.
• _at_see classname
• Creates a hyperlink See Also classname
• _at_since since-text
• Adds a Since entry. Usually used to specify
  that a feature or change exists since the release
  number of the software specified in the
  since-text
• _at_deprecated deprecated-text
• Adds a comment that this method can no longer be
  used. Convention is to describe method that
  serves as replacement
• Example _at_deprecated Replaced by setBounds(int,
  int, int, int).

40
Constructor and Method Doc Tags

• Can contain _at_see tag, _at_since tag, _at_deprecated as
  well as
• _at_param parameter-name description
• Adds a parameter to the "Parameters" section. The
  description may be continued on the next line.
• _at_return description
• Adds a "Returns" section, which contains the
  description of the return value.
• _at_exception fully-qualified-class-name description
  
• Adds a "Throws" section, which contains the name
  of the exception that may be thrown by the
  method. The exception is linked to its class
  documentation.
• _at_see classname
• Adds a hyperlink "See Also" entry to the method.

41
Example of a Class Doc Comment

• /
• A class representing a window on
  the screen.
• For example
• ltpregt
• Window win new
  Window(parent)
• win.show()
• lt/pregt
• _at_author Sami Shaio
• _at_version I, G
• _at_see java.awt.BaseWindow
• _at_see java.awt.Button
• /
• class Window extends BaseWindow
• ...

42
Example of a Method Doc Comment

• /
• Returns the character at the
  specified index. An index
• ranges from ltcodegt0lt/codegt
  to ltcodegtlength() - 1lt/codegt.
• _at_param index the index
  of the desired character.
• _at_return the desired
  character.
• _at_exception
  StringIndexOutOfRangeException
• if the index is
  not in the range ltcodegt0lt/codegt
• to
  ltcodegtlength()-1lt/codegt.
• _at_see
  java.lang.CharactercharValue()
• /
• public char charAt(int index)
• ...

43
Example of a Field Doc Comment

• A field comment can contain only the _at_see, _at_since
  and _at_deprecated tags
• /
• The X-coordinate of the
  window.
• _at_see window1
• /
• int x 1263732

44
Example Specifying a Service in Java

• / Office is a physical structure in a building.
  It is possible to create an instance of a office
  add an occupant get the name and the number of
  occupants /
• public class Office
• / Adds an occupant to the office /
• _at_param NAME name is a nonempty string /
• public void AddOccupant(string name)
• / _at_Return Returns the name of the office.
  Requires, that Office has been initialized with a
  name /
• public string GetName()
• ....

45
Implementation of Application Domain Classes

• New objects are often needed during object
  design
• Use of Design patterns lead to new classes
• The implementation of algorithms may necessitate
  objects to hold values
• New low-level operations may be needed during the
  decomposition of high-level operations
• Example The EraseArea() operation offered by a
  drawing program.
• Conceptually very simple
• Implementation
• Area represented by pixels
• Repair () cleans up objects partially covered by
  the erased area
• Redraw() draws objects uncovered by the erasure
• Draw() erases pixels in background color not
  covered by other objects

46
Application Domain vs Solution Domain Objects
Requirements Analysis (Language of
Application Domain)
Object Design (Language of Solution Domain)
Incident Report
Incident Report
Text box
Menu
Scrollbar
47
Package it all up

• Pack up design into discrete physical units that
  can be edited, compiled, linked, reused
• Construct physical modules
• Ideally use one package for each subsystem
• System decomposition might not be good for
  implementation.
• Two design principles for packaging
• Minimize coupling
• Classes in client-supplier relationships are
  usually loosely coupled
• Large number of parameters in some methods mean
  strong coupling (gt 4-5)
• Avoid global data
• Maximize cohesiveness
• Classes closely connected by associations gt same
  package

48
Packaging Heuristics

• Each subsystem service is made available by one
  or more interface objects within the package
• Start with one interface object for each
  subsystem service
• Try to limit the number of interface operations
  (7-2)
• If the subsystem service has too many operations,
  reconsider the number of interface objects
• If you have too many interface objects,
  reconsider the number of subsystems
• Difference between interface objects and Java
  interfaces
• Interface object Used during requirements
  analysis, system design and object design.
  Denotes a service or API
• Java interface Used during implementation in
  Java (A Java interface may or may not implement
  an interface object)

49
Summary

• Object design closes the gap between the
  requirements and the machine.
• Object design is the process of adding details to
  the requirements analysis and making
  implementation decisions
• Object design includes
• 1. Service specification
• 2. Component selection
• 3. Object model restructuring
• 4. Object model optimization
• Object design is documented in the Object Design
  Document, which can be generated using tools such
  as JavaDoc.

50
Chapter 9,Testing
51
Outline

• Terminology
• Types of errors
• Dealing with errors
• Quality assurance vs Testing
• Component Testing
• Unit testing
• Integration testing
• Testing Strategy
• Design Patterns Testing

• System testing
• Function testing
• Structure Testing
• Performance testing
• Acceptance testing
• Installation testing

52
Terminology

• Reliability The measure of success with which
  the observed behavior of a system confirms to
  some specification of its behavior.
• Failure Any deviation of the observed behavior
  from the specified behavior.
• Error The system is in a state such that further
  processing by the system will lead to a failure.
• Fault (Bug) The mechanical or algorithmic cause
  of an error.
• There are many different types of errors and
  different ways how we can deal with them.

53
What is this?
54
Erroneous State (Error)
55
Algorithmic Fault
56
Mechanical Fault
57
How do we deal with Errors and Faults?
58
Verification?
59
Modular Redundancy?
60
Declaring the Bug as a Feature?
61
Patching?
62
Testing?
63
Examples of Faults and Errors

• Faults in the Interface specification
• Mismatch between what the client needs and what
  the server offers
• Mismatch between requirements and implementation
• Algorithmic Faults
• Missing initialization
• Branching errors (too soon, too late)
• Missing test for nil

• Mechanical Faults (very hard to find)
• Documentation does not match actual conditions
  or operating procedures
• Errors
• Stress or overload errors
• Capacity or boundary errors
• Timing errors
• Throughput or performance errors

64
Dealing with Errors

• Verification
• Assumes hypothetical environment that does not
  match real environment
• Proof might be buggy (omits important
  constraints simply wrong)
• Modular redundancy
• Expensive
• Declaring a bug to be a feature
• Bad practice
• Patching
• Slows down performance
• Testing (this lecture)
• Testing is never good enough

65
Another View on How to Deal with Errors

• Error prevention (before the system is released)
• Use good programming methodology to reduce
  complexity
• Use version control to prevent inconsistent
  system
• Apply verification to prevent algorithmic bugs
• Error detection (while system is running)
• Testing Create failures in a planned way
• Debugging Start with an unplanned failures
• Monitoring Deliver information about state. Find
  performance bugs
• Error recovery (recover from failure once the
  system is released)
• Data base systems (atomic transactions)
• Modular redundancy
• Recovery blocks

66
Some Observations

• It is impossible to completely test any
  nontrivial module or any system
• Theoretical limitations Halting problem
• Practial limitations Prohibitive in time and
  cost
• Testing can only show the presence of bugs, not
  their absence (Dijkstra)

67
Testing takes creativity

• Testing often viewed as dirty work.
• To develop an effective test, one must have
• Detailed understanding of the system
• Knowledge of the testing techniques
• Skill to apply these techniques in an effective
  and efficient manner
• Testing is done best by independent testers
• We often develop a certain mental attitude that
  the program should in a certain way when in fact
  it does not.
• Programmer often stick to the data set that makes
  the program work
• "Dont mess up my code!"
• A program often does not work when tried by
  somebody else.
• Don't let this be the end-user.

68
Testing Activities
Requirements Analysis Document
Subsystem Code
Requirements Analysis Document
Unit
System Design Document
T
est
Tested Subsystem
User Manual
Subsystem Code
Unit
T
est
Integration
Tested Subsystem
Functional
Test
Test
Functioning System
Integrated Subsystems
Tested Subsystem
Subsystem Code
Unit
T
est
All tests by developer
69
Testing Activities ctd
Clients Understanding of Requirements
User Environment
Global Requirements
Accepted System
Validated System
Functioning System
Performance
Acceptance
Installation
Test
Test
Test
Usable System
Tests by client
Tests by developer
Users understanding
System in
Use
Tests (?) by user
70
Fault Handling Techniques
Fault Handling
Fault Avoidance
Fault Tolerance
Fault Detection
Atomic Transactions
Modular Redundancy
Reviews
Design Methodology
Verification
Configuration Management
Debugging
Testing
Correctness Debugging
Performance Debugging
Component Testing
Integration Testing
System Testing
71
Quality Assurance encompasses Testing
Quality Assurance
Usability Testing
Prototype Testing
Scenario Testing
Product Testing
Fault Avoidance
Fault Tolerance
Atomic Transactions
Modular Redundancy
Verification
Configuration Management
Fault Detection
Reviews
Debugging
Walkthrough
Inspection
Testing
Correctness Debugging
Performance Debugging
Component Testing
Integration Testing
System Testing
72
Component Testing

• Unit Testing
• Individual subsystem
• Carried out by developers
• Goal Confirm that subsystems is correctly coded
  and carries out the intended functionality
• Integration Testing
• Groups of subsystems (collection of classes) and
  eventually the entire system
• Carried out by developers
• Goal Test the interface among the subsystem

73
System Testing

• System Testing
• The entire system
• Carried out by developers
• Goal Determine if the system meets the
  requirements (functional and global)
• Acceptance Testing
• Evaluates the system delivered by developers
• Carried out by the client. May involve executing
  typical transactions on site on a trial basis
• Goal Demonstrate that the system meets customer
  requirements and is ready to use
• Implementation (Coding) and testing go hand in
  hand

74
Unit Testing

• Informal
• Incremental coding
• Static Analysis
• Hand execution Reading the source code
• Walk-Through (informal presentation to others)
• Code Inspection (formal presentation to others)
• Automated Tools checking for
• syntactic and semantic errors
• departure from coding standards
• Dynamic Analysis
• Black-box testing (Test the input/output
  behavior)
• White-box testing (Test the internal logic of the
  subsystem or object)
• Data-structure based testing (Data types
  determine test cases)

75
Black-box Testing

• Focus I/O behavior. If for any given input, we
  can predict the output, then the module passes
  the test.
• Almost always impossible to generate all possible
  inputs ("test cases")
• Goal Reduce number of test cases by equivalence
  partitioning
• Divide input conditions into equivalence classes
• Choose test cases for each equivalence class.
  (Example If an object is supposed to accept a
  negative number, testing one negative number is
  enough)

76
Black-box Testing (Continued)

• Selection of equivalence classes (No rules, only
  guidelines)
• Input is valid across range of values. Select
  test cases from 3 equivalence classes
• Below the range
• Within the range
• Above the range
• Input is valid if it is from a discrete set.
  Select test cases from 2 equivalence classes
• Valid discrete value
• Invalid discrete value
• Another solution to select only a limited amount
  of test cases
• Get knowledge about the inner workings of the
  unit being tested gt white-box testing

77
White-box Testing

• Focus Thoroughness (Coverage). Every statement
  in the component is executed at least once.
• Four types of white-box testing
• Statement Testing
• Loop Testing
• Path Testing
• Branch Testing

78
White-box Testing (Continued)

• Statement Testing (Algebraic Testing) Test
  single statements (Choice of operators in
  polynomials, etc)
• Loop Testing
• Cause execution of the loop to be skipped
  completely. (Exception Repeat loops)
• Loop to be executed exactly once
• Loop to be executed more than once
• Path testing
• Make sure all paths in the program are executed
• Branch Testing (Conditional Testing) Make sure
  that each possible outcome from a condition is
  tested at least once

79
White-box Testing Example
FindMean(float Mean, FILE ScoreFile)
SumOfScores 0.0 NumberOfScores 0 Mean 0
/Read in and sum the scores/
Read(Scor
eFile, Score)
while (! EOF(ScoreFile)
if ( Score gt 0.0 )

SumOfScores SumOfScores Score

NumberOfScores


Read(ScoreFile, Score)

/ Compute the mean and print the result /
if (NumberOfScores gt 0 )

Mean SumOfScores/NumberOfScores
printf("The mean score is f \n", Mean)
else
printf("No scores found in file\n")

80
White-box Testing Example Determining the Paths
FindMean (FILE ScoreFile) float SumOfScores
0.0 int NumberOfScores 0 float Mean0.0
float Score Read(ScoreFile, Score) while (!
EOF(ScoreFile) if (Score gt 0.0 ) SumOfScores
SumOfScores Score NumberOfScores Read(S
coreFile, Score) / Compute the mean and print
the result / if (NumberOfScores gt 0) Mean
SumOfScores / NumberOfScores printf( The mean
score is f\n, Mean) else printf (No scores
found in file\n)
81
Constructing the Logic Flow Diagram
82
Finding the Test Cases
Start
1
a (Covered by any data)
2
b
(Data set must contain at least
one value)
3
(Positive score)
d
e
(Negative score)
c
5
4
(Data set must
h
(Reached if either f or
g
f
be empty)
6
e is reached)
7
j
i
(Total score gt 0.0)
(Total score lt 0.0)
9
8
k
l
Exit
83
Test Cases

• Test case 1 ? (To execute loop exactly once)
• Test case 2 ? (To skip loop body)
• Test case 3 ?,? (to execute loop more than once)
• These 3 test cases cover all control flow paths

84
Comparison of White Black-box Testing

• White-box Testing
• Potentially infinite number of paths have to be
  tested
• White-box testing often tests what is done,
  instead of what should be done
• Cannot detect missing use cases
• Black-box Testing
• Potential combinatorical explosion of test cases
  (valid invalid data)
• Often not clear whether the selected test cases
  uncover a particular error
• Does not discover extraneous use cases
  ("features")

• Both types of testing are needed
• White-box testing and black box testing are the
  extreme ends of a testing continuum.
• Any choice of test case lies in between and
  depends on the following
• Number of possible logical paths
• Nature of input data
• Amount of computation
• Complexity of algorithms and data structures

85
The 4 Testing Steps

• 1. Select what has to be measured
• Completeness of requirements
• Code tested for reliability
• Design tested for cohesion
• 2. Decide how the testing is done
• Code inspection
• Proofs
• Black-box, white box,
• Select integration testing strategy (big bang,
  bottom up, top down, sandwich)

• 3. Develop test cases
• A test case is a set of test data or situations
  that will be used to exercise the unit (code,
  module, system) being tested or about the
  attribute being measured
• 4. Create the test oracle
• An oracle contains of the predicted results for a
  set of test cases
• The test oracle has to be written down before the
  actual testing takes place

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Guidance for Test Case Selection

• Use analysis knowledge about functional
  requirements (black-box)
• Use cases
• Expected input data
• Invalid input data
• Use design knowledge about system structure,
  algorithms, data structures (white-box)
• Control structures
• Test branches, loops, ...
• Data structures
• Test records fields, arrays, ...

• Use implementation knowledge about algorithms
• Force division by zero
• Use sequence of test cases for interrupt handler

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Unit-testing Heuristics

• 1. Create unit tests as soon as object design is
  completed
• Black-box test Test the use cases functional
  model
• White-box test Test the dynamic model
• Data-structure test Test the object model
• 2. Develop the test cases
• Goal Find the minimal number of test cases to
  cover as many paths as possible
• 3. Cross-check the test cases to eliminate
  duplicates
• Don't waste your time!

• 4. Desk check your source code
• Reduces testing time
• 5. Create a test harness
• Test drivers and test stubs are needed for
  integration testing
• 6. Describe the test oracle
• Often the result of the first successfully
  executed test
• 7. Execute the test cases
• Dont forget regression testing
• Re-execute test cases every time a change is
  made.
• 8. Compare the results of the test with the test
  oracle
• Automate as much as possible

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Component-Based Testing Strategy

• The entire system is viewed as a collection of
  subsystems (sets of classes) determined during
  the system and object design.
• The order in which the subsystems are selected
  for testing and integration determines the
  testing strategy
• Big bang integration (Nonincremental)
• Bottom up integration
• Top down integration
• Sandwich testing
• Variations of the above
• For the selection use the system decomposition
  from the System Design

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Using the Bridge Pattern to enable early
Integration Testing

• Use the bridge pattern to provide multiple
  implementations under the same interface.
• Interface to a component that is incomplete, not
  yet known or unavailable during testing

Seat Interface (in Vehicle Subsystem)
VIP
Seat Implementation
Simulated Seat (SA/RT)
Stub Code
Real Seat
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Example Three Layer Call Hierarchy
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Integration Testing Big-Bang Approach
Unit Test UI
Dont try this!
Unit Test Billing
System Test PAID
Unit Test Learning
Unit Test Event Service
Unit Test Network
Unit Test Database
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Bottom-up Testing Strategy

• The subsystem in the lowest layer of the call
  hierarchy are tested individually
• Then the next subsystems are tested that call the
  previously tested subsystems
• This is done repeatedly until all subsystems are
  included in the testing
• Special program needed to do the testing, Test
  Driver
• A routine that calls a particular subsystem and
  passes a test case to it

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Bottom-up Integration
Test E
Test B, E, F
Test F
Test A, B, C, D, E, F, G
Test C
Test D,G
Test G
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Pros and Cons of bottom up integration testing

• Bad for functionally decomposed systems
• Tests the most important subsystem last
• Useful for integrating the following systems
• Object-oriented systems
• real-time systems
• systems with strict performance requirements

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Top-down Testing Strategy

• Test the top layer or the controlling subsystem
  first
• Then combine all the subsystems that are called
  by the tested subsystems and test the resulting
  collection of subsystems
• Do this until all subsystems are incorporated
  into the test
• Special program is needed to do the testing, Test
  stub
• A program or a method that simulates the activity
  of a missing subsystem by answering to the
  calling sequence of the calling subsystem and
  returning back fake data.

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Top-down Integration Testing
Test A, B, C, D, E, F, G
Test A, B, C, D
Test A
Layer I
Layer I II
All Layers
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Pros and Cons of top-down integration testing

• Test cases can be defined in terms of the
  functionality of the system (functional
  requirements)
• Writing stubs can be difficult Stubs must allow
  all possible conditions to be tested.
• Possibly a very large number of stubs may be
  required, especially if the lowest level of the
  system contains many methods.
• One solution to avoid too many stubs Modified
  top-down testing strategy
• Test each layer of the system decomposition
  individually before merging the layers
• Disadvantage of modified top-down testing Both,
  stubs and drivers are needed

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Sandwich Testing Strategy

• Combines top-down strategy with bottom-up
  strategy
• The system is view as having three layers
• A target layer in the middle
• A layer above the target
• A layer below the target
• Testing converges at the target layer
• How do you select the target layer if there are
  more than 3 layers?
• Heuristic Try to minimize the number of stubs
  and drivers

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Selecting Layers for the PAID system

• Top Layer
• User Interface
• Middle Layer
• Billing, Learning,Event Service
• Bottom Layer
• Network, Database

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Sandwich Testing Strategy
Test E
Test B, E, F
Bottom Layer Tests
Test F
Test A, B, C, D, E, F, G
Test D,G
Test G
Test A
Top Layer Tests
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Pros and Cons of Sandwich Testing

• Top and Bottom Layer Tests can be done in
  parallel
• Does not test the individual subsystems
  thoroughly before integration
• Solution Modified sandwich testing strategy

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Modified Sandwich Testing Strategy

• Test in parallel
• Middle layer with drivers and stubs
• Top layer with stubs
• Bottom layer with drivers
• Test in parallel
• Top layer accessing middle layer (top layer
  replaces drivers)
• Bottom accessed by middle layer (bottom layer
  replaces stubs)

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Modified Sandwich Testing Strategy
Double Test I
Test B
Test E
Triple Test I
Triple Test I
Test B, E, F
Double Test II
Test F
Test A, B, C, D, E, F, G
Test D
Double Test II
Test D,G
Test G
Test A
Test C
Double Test I
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Scheduling Sandwich Tests Example of a
Dependency Chart
SystemTests
Triple Tests
Unit Tests
Double Tests
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Steps in Component-Based Testing

• 1. Based on the integration strategy, select a
  component to be tested. Unit test all the classes
  in the component.
• 2. Put selected component together do any
  preliminary fix-up necessary to make the
  integration test operational (drivers, stubs)
• 3. Do functional testing Define test cases that
  exercise all uses cases with the selected
  component

• 4. Do structural testing Define test cases that
  exercise the selected component
• 5. Execute performance tests
• 6. Keep records of the test cases and testing
  activities.
• 7. Repeat steps 1 to 7 until the full system is
  tested.
• The primary goal of integration testing is to
  identify errors in the (current) component
  configuration.

.
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Which Integration Strategy should you use?

• Factors to consider
• Amount of test harness (stubs drivers)
• Location of critical parts in the system
• Availability of hardware
• Availability of components
• Scheduling concerns
• Bottom up approach
• good for object oriented design methodologies
• Test driver interfaces must match component
  interfaces
• ...

• ...Top-level components are usually important and
  cannot be neglected up to the end of testing
• Detection of design errors postponed until end
  of testing
• Top down approach
• Test cases can be defined in terms of functions
  examined
• Need to maintain correctness of test stubs
• Writing stubs can be difficult

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System Testing

• Functional Testing
• Structure Testing
• Performance Testing
• Acceptance Testing
• Installation Testing
• Impact of requirements on system testing
• The more explicit the requirements, the easier
  they are to test.
• Quality of use cases determines the ease of
  functional testing
• Quality of subsystem decomposition determines the
  ease of structure testing
• Quality of nonfunctional requirements and
  constraints determines the ease of performance
  tests

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Structure Testing

• Essentially the same as white box testing.
• Goal Cover all paths in the system design
• Exercise all input and output parameters of each
  component.
• Exercise all components and all calls (each
  component is called at least once and every
  component is called by all possible callers.)
• Use conditional and iteration testing as in unit
  testing.

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Functional Testing
.

• Essentially the same as black box testing
• Goal Test functionality of system
• Test cases are designed from the requirements
  analysis document (better user manual) and
  centered around requirements and key functions
  (use cases)
• The system is treated as black box.
• Unit test cases can be reused, but in end user
  oriented new test cases have to be developed as
  well.

.
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Performance Testing

• Timing testing
• Evaluate response times and time to perform a
  function
• Environmental test
• Test tolerances for heat, humidity, motion,
  portability
• Quality testing
• Test reliability, maintain- ability
  availability of the system
• Recovery testing
• Tests systems response to presence of errors or
  loss of data.
• Human factors testing
• Tests user interface with user

• Stress Testing
• Stress limits of system (maximum of users, peak
  demands, extended operation)
• Volume testing
• Test what happens if large amounts of data are
  handled
• Configuration testing
• Test the various software and hardware
  configurations
• Compatibility test
• Test backward compatibility with existing systems
• Security testing
• Try to violate security requirements

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Test Cases for Performance Testing

• Push the (integrated) system to its limits.
• Goal Try to break the subsystem
• Test how the system behaves when overloaded.
• Can bottlenecks be identified? (First candidates
  for redesign in the next iteration
• Try unusual orders of execution
• Call a receive() before send()
• Check the systems response to large volumes of
  data
• If the system is supposed to handle 1000 items,
  try it with 1001 items.
• What is the amount of time spent in different use
  cases?
• Are typical cases executed in a timely fashion?

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Acceptance Testing

• Goal Demonstrate system is ready for operational
  use
• Choice of tests is made by client/sponsor
• Many tests can be taken from integration testing
• Acceptance test is performed by the client, not
  by the developer.
• Majority of all bugs in software is typically
  found by the client after the system is in use,
  not by the developers or testers. Therefore two
  kinds of additional tests

• Alpha test
• Sponsor uses the software at the developers
  site.
• Software used in a controlled setting, with the
  developer always ready to fix bugs.
• Beta test
• Conducted at sponsors site (developer is not
  present)
• Software gets a realistic workout in target
  environ- ment
• Potential customer might get discouraged

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Testing has its own Life Cycle
Establish the test objectives
Design the test cases
Write the test cases
Test the test cases
Execute the tests
Evaluate the test results
Change the system
Do regression testing
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Test Team
Professional Tester
too familiar
Programmer
with code
Analyst
System Designer
Test
User
Team
Configuration Management Specialist
115
Summary

• Testing is still a black art, but many rules and
  heuristics are available
• Testing consists of component-testing (unit
  testing, integration testing) and system testing
• Design Patterns can be used for component-based
  testing
• Testing has its own lifecycle