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Software Testing and Quality Assurance

Lecture 8 - Software Testing Techniques

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Lecture Outline Discuss testing techniques based on

achieving coverage of the software. Control-flow testing Data-flow testing

Static Data-flow testing

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Coverage Based Testing To achieve some form of coverage of

the program-under- test based on well-defined-criteria Rather than partitioning the input domain of

the program.

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Control-flow Testing Aims to understand the flow of control within

a program. Select test inputs to exercise paths in the Control-

Flow Graph (CFG). Paths are selected based on the control

information in the graph. Examples of coverage criteria include:

Path coverage Branch coverage condition coverage

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Control-flow Graphs Control-flow is a graph G = (V,E) where;

Vertex represents a program statement Edge represents the ability of a program to

flow from its current statement to the next statement.

If an edge is associated with a conditional statement, label the edge with the conditional value, either true or false.

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Control-flow Graphs - ExampleInt power (int base, int n){

int power i;power = 1;for (i = 1; I ≤ n; i ++) {

power = base * power;}

Return power;}

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Control-flow Graphs - Example

int base, int n

int power, 1

Power = 1

i = 1

I ≤ n Power = base * power

i = i + 1

return power

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Branch or decision

Control-flow Graphs - Example

int base, int n

int power, 1

Power = 1

i = 1

I ≤ n Power = base * power

i = i + 1

return power

Execution Path Condition

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Coverage Based Criteria Statement - every statement of the program

should be exercised at least once. Branch coverage - every possible alternative

in a branch of the program should be tested at least once.

Condition coverage - each condition in a branch is made to evaluate to true or false.

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Coverage Based Criteria Multiple condition coverage

All possible combinations of condition outcomes within each branch should be exercised at least once.

For example, if (a&&b) --- evaluate all possible combinations.

Path coverage Every execution path of the program

should be exercised at least once.

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Data-Flow Testing Despite analysis of input and output

domains used in Equivalence partitioning, boundary value

analysis, and control flow Testing relies on personal experience to

choose test cases.

For example, program with 5 input variables3125 possible EC

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Data-Flow Testing Information about the creation and use

of data definitions in a program. Detect many single programming or logical

faults in the program; Provide testers with dependencies

between the definitions and use of variables.

Complement coverage based testing.

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Static Data-Flow Testing Simplest form of data-flow analysis A programming language statement can

act on a variable in 3 different ways. Define a variable Reference a variable Undefined a variable

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Static Data-Flow Testing - Define (d) A statement defines a variable by

assigning a value to a variable. For example,

x = 5; Scan (x);

x = 3 * y;

Defined the variable x

Only defined the variable xIf y is declared and defined.

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Static Data-Flow Testing - Reference (r) A statement makes a reference to a variable

either as an: I-value - variable, array cell into which values can

be stored. A variable that appears on the left hand side of an

assignment statement. R -value - any variable that must be referenced to

get its value. A variable that appears on the right hand side of an

assignment statement.

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Static Data-Flow Testing - Un-define (u) A statement un-defines a variable

whenever the value of the variable becomes unknown.

For example, The scope of a local variable ends.

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Static Data-Flow Testing - Anomalies u-r anomaly

Undefined variable is referenced. For example, un-initialized variable.

d-u anomaly A defined variable has not been referenced before

it becomes undefined. d-d anomaly

Same variable is defined twice. Usually due to misspelling or because variables

have been imported from another function.

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Int i,j; int *c;

C = malloc(….)

c = Null

C [0] = 1; c[1] = 1; sum = 2;

Error (….)

i = 2

I ≤ n

C [i] = c[I-1] + c[I-2]; sum += c[I];

Return sum;

Fee (c)

I++

A

B

C

True

DFalse

E

F

GH False

I

J

K

Action on variable cNo action

Define

reference

No action

reference

Un-define

No action

u-r anomaly

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Key points Control-Flow Testing aims to understand the

flow of control within a program. Most common - Control-Flow Graph

Data-Flow Testing Provides additional information to use for program

analysis and testing. Static Data-Flow Analysis

Typing errors Un-initialized variables, Misspelling of names etc.

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Announcement Quiz 2 moved from

Wednesday 29/10/2008 to Saturday 01/11/2008.

Material Lec 6, Lec 7,Lec 8 & Lec 9