Software testing techniques
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Software Testing Techniques. Software Testing. Testing is the process of exercising a program with the specific intent of finding errors prior to delivery to the end user. Software Development Process. Tangible Product. Abstract Concept. Testing. Tries hard to demolish the software.

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Software Testing Techniques

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Software testing techniques

Software Testing Techniques

Software testing

Software Testing

Testing is the process of exercising a

program with the specific intent of finding

errors priorto delivery to the enduser.

Software development process

Software Development Process

Tangible Product




Tries hard to demolish the software

Developer must discard the preconceived idea that his software is always correct

Developer must discard the preconceived idea that his software is always correct.

Software testing objectives

Software Testing Objectives

  • Uncovering different cases of errors

  • Needing minimum effort and time

  • Showing that software functions work according to specification

It cannot showabsence of errors or defects. It can only show that errors are present

Software testing principles

Customer thinks - most serious defect is not meeting his requirements

Software Testing Principles

All tests can be planned and designed before any coding begins

  • All tests should be traceable to customer requirements

  • Tests should be planned long before testing begins

  • The “pareto” principle applies to software testing

  • Exhaustive testing is not possible

  • To be most effective, testing should be conducted by a third party

80 % of errors originate from 20% of programs

Too many paths in a normal -size program

Who tests the software

Who Tests the Software?


independent tester

Understands the system

Must learn about the system,

but, will test "gently"

but, will attempt to break it

and, is driven by quality

and, is driven by "delivery"

What is a good test

What is a GOOD Test?

Has a high probability of finding an error

It must not be redundant. Every test must have a different purpose

It should neither be too simple, nor too complex.

What testing shows

What Testing Shows


requirements conformance


an indication

of quality



  • Operability—it operates cleanly

  • Observability—the results of each test case are readily observed

  • Controlability—the degree to which testing can be automated and optimized

  • Decomposability—testing can be targeted

  • Simplicity—reduce complex architecture and logic to simplify tests

  • Stability—few changes are requested during testing

  • Understandability—of the design

Test case design

Test Case Design

  • Design of test cases is as challenging asdesigning the software itself

  • A rich variety of test case design methods have evolved

  • Methods provide a systematic approach o testing

  • Methods provide a mechanism for that ensures the completeness of tests and high likelihood of finding an error

Software testing1

Software Testing

black-box methods





White box testing

White Box Testing

  • Close examination of procedural detail

  • Logical paths through the software are tested by providing test cases that exercise specific sets of conditions and/or loops

  • Status of the program is examined at various points to determine if the actual status matches the expected status

Does white box testing lead to 100 correct program

Does White Box Testing lead to 100% correct program?

The answer is: No

It is not possible to exhaustively test every program path because the number paths is simply too large

Exhaustive testing

Exhaustive Testing

loop < 20 X


There are10 possible paths! If we execute one

test per millisecond, it would take 3,170 years to

test this program!!

Selective testing

Selective Testing

Selected path

loop < 20 X

Black box testing

Black Box Testing

  • Know the specific function that the program is designed to perform

  • Test that each function is fully operational

  • Search for more errors in the functions

  • These tests are conducted at the software interface

  • Whether input is properly accepted and output is correctly produced

  • Integrity of external information (database) is maintained

  • Examines fundamental aspects of the system with little regard to internal logical structure

Software testing techniques

The attributes of both black-box and white-box testing can be combined to provide an approach that validates the software interface and selectively ensures that the internal workings of the software are correct

White box testing1

White Box Testing

  • Is also known as “Glass Box Testing”

  • Uses the control structure of the procedural design to derive test cases

If a= b then

do c


do v

Glass Box

White box testing2

WhiteBox Testing

Guarantees that all independent paths within a module have been exercised at least once

Exercise all logical decisions on their true and false sides

Exercise all loops at their boundaries and within their operational bounds

Exercise internal data structures to ensure their validity

Test case design1

Test Case Design

"Bugs lurk in corners

and congregate at

boundaries ..."

Boris Beizer


to uncover errors


in a complete manner


with a minimum of effort and time

Why cover

Why Cover?

logic errors and incorrect assumptions

are inversely proportional to a path's

execution probability

we often


that a path is not

likely to be executed; in fact, reality is

often counter intuitive

typographicalerrors are random; it's

likely that untested paths will contain


Why need white box testing

Why need White-box testing?

  • Logic errors occur more frequently in the less probable paths of execution

  • Everyday processing tends to be well understood while “special case “ processing tends to fall into cracks

  • We often believe that a logical path is not likely to be executed when , in fact it may be executed on a regular basis

  • Typos are random. It is as likely that a type will exist on an obscure logical path as on a mainstream path.

White box testing3

White-Box Testing

... our goal is to ensure that all

statements and conditions have

been executed at least once ...

Basis path testing

Basis Path Testing

  • It is white-box testing technique

  • Proposed by Tom Macabe

  • Derives a logical complexity measure

  • Test cases derived to exercise the basis set are guaranteed to execute every statement in the program at least once during testing

  • Uses flow-graph notation

  • Each structured construct has corresponding flow graph symbol

Structured constructs

Structured Constructs








Repeat until



Flow graph symbols

Flow Graph Symbols






Flow graph symbols1

Flow Graph Symbols

  • Each circle is called a flow graph node , represents one or more procedural statements

  • A sequence of process boxes and a decision diamond can map into a single node

  • An edge (arrow) must terminate at a node

  • Areas bounded by edged and nodes are called regions

  • Area outside graph is also a region

Flow graph for compound conditions

Flow Graph for Compound Conditions


  • A compound condition occurs when one or more Boolean operators (AND,OR) is present in a conditional statement

  • Separate node is created for each condition

  • Each condition node is known as predicate node

  • Each predicate node has two or more edges leaving it





If a or b thenprocedure x


procedure y


Cyclomatic complexity

Cyclomatic Complexity

  • Very useful software metric

  • Foundation on graph theory

  • Quantitative measure of the logical complexity of the program

  • It defines the number of independent paths in the basis set of a program

  • Provides s with an upper bound for the number of tests to be conducted

  • Ensures that all statements have been executed at least once

Cyclomatic complexity1

Cyclomatic Complexity

A number of industry studies have indicated

that the higher V(G), the higher the probability

or errors.



modules in this range are

more error prone

Computation of cyclomatic complexity v g for flow graph g

There are three ways:

Computation of Cyclomatic Complexity V(G) for flow - graph G

V(G) = P+1


P - no. of predicate nodes in G

V(G) = E - N + 2


W - no. of edges in G

N - no. of nodes in G

V(G) = R


R- no. of regions in G

Given flow-graph has 4 regions

V(G) = 11-9 + 2 = 4

V(G) = 3 + 1 = 4

Independent path

Independent Path

  • Any path through the program that introduces at least one new set of processing statements or a new condition

  • Must move along at least one edge that has not been traversed before the path is defined

  • Each path introduces a new edge

  • There are Four paths for the given example:

    • Path 1: 1-11

    • Path 2: 1-2-3-4-5-10-1-11

    • Path-3: 1-2-3-6-8-9-10-1-11

    • Path 4: 1-2-3-6-7-9-10-1-11

Basis path testing1









Basis Path Testing

Next, we derive the

independent paths:

Since V(G) = 4,

there are four paths

Path 1: 1,2,3,6,7,8

Path 2: 1,2,3,5,7,8

Path 3: 1,2,4,7,8

Path 4: 1,2,4,7,2,4,...7,8

Finally, we derive test

cases to exercise these


Deriving test cases

Deriving Test Cases

  • Using the code as the foundation , draw a corresponding flow graph

  • Determine the cyclomatic complexity of the flow graph

  • Determine a basis set of linearly independent paths

  • Prepare test cases that will force execution of each path in the basis set

  • Execute each test case and compared to expected results

  • Some paths cannot be tested independently and must be tested as part of another path

Condition testing

Condition Testing

  • It is a design method that exercises the logical conditions (Consisting of arithmetic, relational and Boolean expressions and operators) in a program module

  • Types of error found in a condition:

    • Boolean operator error

    • Boolean variable error

    • Boolean parenthesis error

    • Relational operator error

    • Arithmetic expression error

Condition testing1

Condition Testing

  • Branch Testing

    • For a compound condition C, the true and false branches of C and every simple condition in C need to be executed at least once

  • Domain Testing

    • Requires three or four tests for a relational expression

    • To detect errors in E1<relational-operator>E2

      • three tests are required to detect error in the operator

      • putting as minimum possible different values in E1 and E2 will help to detect errors in E1and E2

Bro testing

BRO Testing

  • All relational operators and boolean variables must occur only once

  • Uses condition constraint for a condition C which is defined as (D1, D2, …Dn) where Dispecifies thea constraint on he outcome of ith condition of C

  • Boolean variables have constraint value True or False

  • For relational expression symbols <,>, = are used to specify the conditions

Bro testing examples

BRO Testing - Examples

Example 1: B1 & B2

C1= (D1,D2) = {(t,t),(t,f),(f,t)}

Example 2: B1 & (E3=E4)

C2= (D1,D2) = {(t,=),(t,>),(t,<),(f,=)}

Example 3: (E1 > E2) & (E3=E4)

C2= (D1,D2) = {(>,=),(<,=),(>,>),(>,<),(=,=)}

Dataflow testing

Dataflow Testing

  • Selects test paths according to the location of definitions and uses of variables in the program (S-statement no.)

  • DEF(S) = {X| statement S contains a definition of X} USE(S) = (X| statement S contains a use of X} Assume

  • For if or loop statement DEF set is always empty

  • The definition of var X at S is said to be live at statement S’ if the path S-S’ contains no other definition of X

  • A definition-use chain of var Xis of the form [X,S,S’] where X is DEF(S) and USE(S’) and X is live at S’.

Du testing

DU Testing

  • Every DU chain should be covered at least once

  • Useful for programs with nested if and loop statements

  • Effective for error-detection

  • Selecting test-paths is quite difficult

  • Does not guarantee all branches of a program (e.g. if statement with no else statement and no definition in the then part.

Du testing1

DU Testing

proc x


do while C1

if C2


if C4

then B4;

else B5;



if C3

then B2;

else B3;





end proc;

Var X is defined in the last statement of blocks B1, B2, B3, B4, B5 and used in the first statements of B2, B3, B4, B5, B6

There are 25 DU chains of var X

We need to cover only five paths from each B1, B2, B3, B4, B5 to B6

Loop testing

Loop Testing

  • Loops are he cornerstone of vast majority of all software

  • Focuses exclusively on the validity of loop constructs

  • Four different classes of loops are defined:

    • Simple loops

    • Nested loops

    • concatenated loops

    • unstructured loops

Loop testing1

Loop Testing









Simple loops

Simple Loops

Set of Tests

  • Skip the loop entirely

  • Only one pass through the loop

  • Two passes through the loop

  • M passes through the loop where m < n (n – max no. pf allowable passes)

  • N-1, n, n+1 passes throughthe loop

Nested loops

Nested Loops

Number of possible test is impractically large if simple loop approach is adopted.

  • Start at the innermost loop. Set allother loops to minimum value

  • Conduct simple loop test for the innermost loop while outer loops have the minimum loop counter

  • Work outward, conducting tests for the next loop , keeping outer loops at minimum value and nested loops at typical values

  • Continue until all loops have been tested

Concatenated loops

Concatenated Loops

  • Simple loop approach can be adopted if each of the loops is independent of the others

  • If loop counter value of one loop is used as the initial loop counter value of another, then the loops are not independent. In such cases nested loop approach should be adopted

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