Chapter 8 Testing the Programs Shari L. Pfleeger Joann M. Atlee 4 th Edition

Chapter 8

Testing the Programs

Shari L. PfleegerJoann M. Atlee

4th Edition

Pfleeger and Atlee, Software Engineering: Theory and Practice

Chapter 8.2

Contents

8.1 Software Faults and Failures8.2 Testing Issues8.3 Unit Testing8.4 Integration Testing8.5 Testing Object Oriented Systems8.6 Test Planning8.7 Automated Testing Tools8.8 When to Stop Testing8.9 Information System Example8.10 Real Time Example8.11 What this Chapter Means for You


Chapter 8.3

Chapter 8 Objectives

• Types of faults and how to classify them• The purpose of testing• Unit testing• Integration testing strategies• Test planning• When to stop testing


Chapter 8.4

8.1 Software Faults and FailuresWhy Does Software Fail?

• A wrong or missing requirement– Not what the customer wants or needs

• A requirement that is impossible to implement– Given prescribed hardware and software

• A faulty system design– A database design restrictions

• A faulty program design• The program code may be wrong


Chapter 8.5

8.1 Software Faults and Failures Objective of Testing

• Objective of testing: discover faults• A test is successful only when a fault is discovered

– Fault identification is the process of determining what fault(s) caused the failure

– Fault correction is the process of making changes to the system so that the faults are removed


Chapter 8.6

8.1 Software Faults and FailuresTypes of Faults

• Algorithmic fault or syntax faults– A component’s logic doesn’t produce proper output

• Computation and precision faults– A formula’s implementation is wrong

• Documentation faults– The documentation doesn’t match what a program does

• Stress or overload faults– Data structures filled past their specified capacity

• Capacity or boundary faults– The system’s performance becomes unacceptable as activity reaches its

specified limit


Chapter 8.7

8.1 Software Faults and FailuresTypes of Faults (continued)

• Timing or coordination faults– Code executing in improper timing

• Performance faults– System does not perform at the speed prescribed

• Recovery Faults– Failures don’t behave as required

• Hardware and system software faults– Supplied hardware and system software do not work

according to the documented conditions and procedures• Standard and procedure faults

– Code doesn’t follow organizational or procedural standards


Chapter 8.8

8.1 Software Faults and FailuresTypical Algorithmic Faults

• An algorithmic fault occurs when a component’s algorithm or logic does not produce proper output– Branching too soon– Branching too late– Testing for the wrong condition– Forgetting to initialize variable or set loop invariants– Forgetting to test for a particular condition– Comparing variables of inappropriate data types

• Syntax faults


Chapter 8.9

8.1 Software Faults and FailuresOrthogonal Defect Classification

• Historical information leads to trends• Trends can lead to changes in designs or requirements

– Leading to reduced number of faults injected

• How:– Categorize faults using IBM Orthogonal Classifications

• Track faults of omission and commission also– Must be product- and organization-independent– Scheme must be applicable to all development stages


Chapter 8.10

8.1 Software Faults and FailuresOrthogonal Defect Classification

Fault Type Meaning

Function Fault that affects capability, end-user interface, product interface with hardware architecture, or global data structure

Interface Fault in interacting with other component or drivers via calls, macros, control, blocks or parameter lists

Checking Fault in program logic that fails to validate data and values properly before they are used

Assignment Fault in data structure or code block initialization

Timing/serialization Fault in timing of shared and real-time resources

Build/package/merge Fault that occurs because of problems in repositories management changes, or version control

Documentation Fault that affects publications and maintenance notes

Algorithm Fault involving efficiency or correctness of algorithm or data structure but not design


Chapter 8.11

8.1 Software Faults and FailuresSidebar 8.1 Hewlett-Packard’s Fault Classification


Chapter 8.12

8.1 Software Faults and FailuresSidebar 8.1 Faults for one Hewlett-Packard Division


Chapter 8.13

8.2 Testing IssuesTest Organization

• Module testing, component testing, or unit testing• Integration testing• Function testing• Performance testing• Acceptance testing• Installation testing• System testing


Chapter 8.14

8.2 Testing IssuesTesting Organization Illustrated


Chapter 8.15

8.2 Testing IssuesAttitude Toward Testing

• The problem:– In academia students are given a grade for the correctness

and operability of their programs– Test cases generated to show correctness– Critiques of program are considered critiques of ability

• The solution:– Egoless programming; programs are viewed as components

of a larger system, not as the property of those who wrote them

– Development team focused on correcting faults, not placing blame


Chapter 8.16

8.2 Testing IssuesWho Performs the Test?

• Independent test team– Avoid conflict for personal responsibility for faults– Improve objectivity between design and implementation– Allow testing and coding concurrently


Chapter 8.17

8.2 Testing IssuesViews of the Test Objects

• Closed box or black box– Functionality of the test objects – No view of code or data structure – input and output only

• Clear box or white box– Structure of the test objects – Internal view of code and data structures


Chapter 8.18

8.2 Testing IssuesClear Box

• Example of logic structure


Chapter 8.19

8.2 Testing IssuesFactors Affecting the Choice of Test Philosophy

• White box or Black box testing– The number of possible logical paths– The nature of the input data– The amount of computation involved– The complexity of algorithms

• Don’t have to chose!– Combination of each could be the right approach


Chapter 8.20

8.3 Unit TestingCode Review

• Code walkthrough– Present code and documentation to review team– Team comments on correctness– Focus is on the code not the coder– No influence on developer performance

• Code inspection– Check code and documentation against list of concerns– Review correctness and efficiency of algorithms– Check comments for completeness– Formalized process


Chapter 8.21

8.3 Unit TestingTypical Inspection Preparation and Meeting Times

Development Artifact Preparation Time Meeting Time

Requirement Document

25 pages per hour 12 pages per hour

Functional specification 45 pages per hour 15 pager per hour

Logic specification 50 pages per hour 20 pages per hour

Source code 150 lines of code per hour

75 lines of code per hour

User documents 35 pages per hour 20 pages per hour


Chapter 8.22

8.3 Unit TestingFault Discovery Rate

Discovery ActivityFault Found per

Thousand

Lines of Code

Requirements review 2.5

Design Review 5.0

Code inspection 10.0

Integration test 3.0

Acceptance test 2.0


Chapter 8.23

8.3 Unit TestingSidebar 8.3 The Best Team Size for Inspections

• The preparation rate, not the team size, determines inspection effectiveness

• The team’s effectiveness and efficiency depend on their familiarity with their product


Chapter 8.24

8.3 Unit TestingProving Code Correct

• Formal proof techniques– Write assertions to describe input\output conditions– Draw a flow diagram depicting logical flow– Generate theorems to be proven– Locate loops and define if-then assertions for each

– Identify all paths from A1 to An

– Cover each path so that each input assertion implies an output assertion

– Prove that the program terminates

• Only proves design is correct, not implementation• Expensive


Chapter 8.25

8.3 Unit TestingProving Code Correct (continued)

• Symbolic execution– Execution using symbols not data variables– Execute each line, checking for state– Program is viewed as a series of state changes

• Automated theorem-proving– Prove software is correct by developing tools to execute it

• The input data and conditions• The output data and conditions• The lines of code for the component to be tested


Chapter 8.26

8.3 Unit TestingProving Code Correct: An Illustration


Chapter 8.27

8.3 Unit TestingTesting versus Proving

• Proving: – Hypothetical environment– Code is viewed as classes of data and conditions– Proof may not involve execution

• Testing: – Actual operating environment– Demonstrate actual use of program– Series of experiments


Chapter 8.28

8.3 Unit TestingSteps in Choosing Test Cases

• Determining test objectives– Coverage criteria

• Selecting test cases– Inputs that demonstrate the behavior of the code

• Defining a test – Detailing execution instructions


Chapter 8.29

8.3 Unit TestingTest Thoroughness

• Statement testing• Branch testing• Path testing• Definition-use testing• All-uses testing• All-predicate-uses/some-computational-uses testing• All-computational-uses/some-predicate-uses testing


Chapter 8.30

8.3 Unit TestingRelative Strengths of Test Strategies


Chapter 8.31

8.3 Unit TestingComparing Techniques

• Fault discovery Percentages by Fault Origin

Discovery Techniques

Requirements

Design Coding Documentation

Prototyping 40 35 35 15

Requirements review 40 15 0 5

Design Review 15 55 0 15

Code inspection 20 40 65 25

Unit testing 1 5 20 0


Chapter 8.32

8.3 Unit TestingComparing Techniques (continued)

• Effectiveness of fault-discovery techniques

Requirements Faults Design Faults

Code Faults

Documentation Faults

Reviews Fair Excellent Excellent Good

Prototypes Good Fair Fair Not applicable

Testing Poor Poor Good Fair

Correctness Proofs Poor Poor Fair Fair


Chapter 8.33

8.3 Unit TestingSidebar 8.4 Fault Discovery Efficiency at Contel IPC

• 17.3% during inspections of the system design• 19.1% during component design inspection• 15.1% during code inspection• 29.4% during integration testing• 16.6% during system and regression testing• 0.1% after the system was placed in the field


Chapter 8.34

8.4 Integration Testing

• Bottom-up• Top-down• Big-bang• Sandwich testing• Modified top-down• Modified sandwich


Chapter 8.35

8.4 Integration TestingTerminology

• Component Driver: a routine that calls a particular component and passes a test case to it

• Stub: a special-purpose program to simulate the activity of the missing component


Chapter 8.36

8.4 Integration TestingView of a System

• System viewed as a hierarchy of components


Chapter 8.37

8.4 Integration TestingBottom-Up Integration Example

• The sequence of tests and their dependencies


Chapter 8.38

8.4 Integration TestingTop-Down Integration Example

• Only A is tested by itself


Chapter 8.39

8.4 Integration Testing Modified Top-Down Integration Example

• Each level’s components individually tested before the merger takes place


Chapter 8.40

8.4 Integration Testing Bing-Bang Integration Example

• Requires both stubs and drivers to test the independent components


Chapter 8.41

8.4 Integration Testing Sandwich Integration Example

• Viewed system as three layers


Chapter 8.42

8.4 Integration Testing Modified Sandwich Integration Example

• Allows upper-level components to be tested before merging them with others


Chapter 8.43

8.4 Integration TestingComparison of Integration Strategies

Bottom-up

Top-down

Modified top-down

Bing-bang Sandwich Modified sandwich

Integration Early Early Early Late Early Early

Time to basic working program

Late Early Early Late Early Early

Component drivers needed

Yes No Yes Yes Yes Yes

Stubs needed No Yes Yes Yes Yes Yes

Work parallelism at beginning

Medium Low Medium High Medium High

Ability to test particular paths

Easy Hard Easy Easy Medium Easy

Ability to plan and control sequence

Easy Hard Hard Easy Hard hard


Chapter 8.44

8.4 Integration TestingSidebar 8.5 Builds at Microsoft

• The feature teams synchronize their work by building the product and finding and fixing faults on a daily basis


Chapter 8.45

8.5 Testing Object-Oriented SystemsTesting the Code

• Questions at the Beginning of Testing OO Systems– Is there a path that generates a unique result?– Is there a way to select a unique result?– Are there useful cases that are not handled?

• Check objects for excesses and deficiencies– Missing objects– Unnecessary classes– Missing or unnecessary associations– Incorrect placement of associations or attributes


Chapter 8.47

8.5 Testing Object-Oriented SystemsEasier and Harder Parts of Testing OO Systems

• OO unit testing is less difficult, but integration testing is more extensive


Chapter 8.48

8.5 Testing Object-Oriented SystemsDifferences Between OO and Traditional Testing

• The farther the gray line is out, the more the difference


Chapter 8.49

8.6 Test Planning

• Establish test objectives• Design test cases• Write test cases• Testing test cases• Execute tests• Evaluate test results


Chapter 8.50

8.6 Test PlanningPurpose of the Plan

• Test plan explains– who does the testing– why the tests are performed– how tests are conducted– when the tests are scheduled

• Test plan describes– That the software works correctly and is free of faults– That the software performs the functions as specified

• The test plan is a guide to the entire testing activity


Chapter 8.51

8.6 Test PlanningContents of the Plan

• What the test objectives are• How the test will be run• Criteria to determine that testing is complete• Detailed list of test cases• How test data is generated• How output data will be captured• Complete picture of how and why testing will be

performed


Chapter 8.52

8.7 Automated Testing Tools

• Code analysis– Static analysis

• code analyzer• structure checker• data analyzer• sequence checker

• Output from static analysis


Chapter 8.53

8.7 Automated Testing Tools (continued)

• Dynamic analysis– program monitors: watch and report program’s behavior

• Test execution– Capture and replay – Stubs and drivers– Automated testing environments

• Test case generators


Chapter 8.54

8.8 When to Stop TestingMore faulty?

• Probability of finding faults during development

• Make it hard to tell when we are done testing…


Chapter 8.55

8.8 When to Stop TestingStopping Approaches

• Fault seeding– Intentionally inserts a known number of faults– Undiscovered faults leads to total faults :

detected seeded Faults = detected nonseeded faults total seeded faults total nonseeded faults

– Improved by basing number of seeds on historical data– Improved by using two independent test groups

• Comparing results

• Coverage Criteria– Determine how many statement, path or branch tests are

required– Use total to track completeness of tests


Chapter 8.56

8.8 When to Stop TestingStopping Approaches (continued)

• Confidence in the software– Based on fault estimates to find confidence

• e.g. 95% confident the software is fault free

C = 1, if n > N= S/(S – N + 1) if n ≤ N

• Where S = number of seeds N = number of actual faults n = number of found faults

• Assumes all faults have equal probability of being detected


Chapter 8.57

8.8 When to Stop TestingIdentifying Fault-Prone Code

• Track the number of faults found in each component during the development

• Collect measurement (e.g., size, number of decisions) about each component

• Classification trees: a statistical technique that sorts through large arrays of measurement information and creates a decision tree to show best predictors– A tree helps in deciding the which components are likely to

have a large number of errors


Chapter 8.58

8.8 When to Stop TestingAn Example of a Classification Tree


Chapter 8.59

8.9 Information Systems ExamplePiccadilly System

• Test strategy that exercises every path• Test scripts describe input and expected outcome• If actual outcome is equal to expected outcome

– Is the component fault-free?– Are we done testing?

• Use data-flow testing strategy rather than structural– Definition-use testing – Ensure each path is exercised


Chapter 8.60

8.10 Real-Time ExampleThe Ariane-5 System

• The Ariane-5’s flight control system was tested in four ways– equipment testing– on-board computer software testing– staged integration– system validation tests

• The Ariane-5 developers relied on insufficient reviews and test coverage


Chapter 8.61

8.11 What this Chapter Means for You

• It is important to understand the difference between faults and failures

• The goal of testing is to find faults, not to prove correctness

• Describes techniques for testing • Absence of faults doesn’t guarantee correctness

Documents

Chapter 8 Testing the Programs Shari L. Pfleeger Joann M. Atlee 4 th Edition