Black Box Testing

BLACK BOX TESTING

Csci 565

Chapters 5-7

Objectives

•Systematic Specification-based testing•Decision Table-Based Testing•Cause-Effect Graphs in Functional testing

•Equivalence Partitioning and Boundary value Analysis

•Input validation and Syntax-driven Testing

Black box testing

•Black box testing•Also known as data-driven or input/output driven testing

•Views the software as a black box•Aims at finding cases in which the software does not behave according to its specifications or requirements•Test data are derived from the specifications

•(no need for taking advantage of knowledge of code)

•The main criterion is exhaustive input testing!!!!

Decision table-based Testing (DTT)•Applicable to the software requirements written using “if-then” statements

•Can be automatically translated into code•Conditions = inputs•Actions = outputs•Rules = test cases

•Assume the independence of inputs

•Example• If cond1 AND cond2 OR cond3 then Action1

Sample of Decision table

A decision table consists of a number of columns (rules) that comprise all test situations

Action ai will take place if c1 and c2 are true

Example: the triangle problem C1: a, b,c form a triangle C2: a=b C3: a= c C4: b= c A1: Not a triangle A2:scalene A3: Isosceles A4:equilateral A5: impossible

r1 r2 … rn

C1 1 1 0

c2 1 1 0

C3 - 1 1

C4 - 1 0

A1 1 0 0

A2 0 0 1

A3 0 0 0

A4 0 1 1

A5 0 0

Test cases from Decision TablesTest Case ID a b c Expected

output

DT1 4 1 2 Not a Triangle

DT2 2888 2888 2888 Equilateral

DT3 ? | ) Impossible

DT4

…

DTn

Example: Simple editor

•A simple text editor should provide the following features•Copy•Paste•Boldface•Underline

r1

r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15 r16

copy 1

paste 0

Undrln 0

Bold 0

Cpy-test

1

Pst-text

0

Und-text

0

Bld-text

0

In general, for n conditions, we need 2n rules

Decision tables as a basis for test case designThe use of decision-table model to design test

cases is applicable The spec is given by table or is easily converted to one The order in which the conditions are evaluated does

not affect the interpretation of rules or the resulting action

The order in which the rules are evaluated does not affect the resulting action

Once a rule has been satisfied and an action is selected, no other rule need be examined

If multiple actions result from the satisfaction of a rule, the order in which the actions take place is not important

Inconsistency problem and nondeterministic table When two rules with same conditions elevated to two different actions

then the whole decisions tables is nondeterministic because it is difficult to decide which rule should be applied

The implications of rules

The above conditions have the following implicationsRules are complete (i.e., every

combination of decision table values including default combinations are inherent in the decision table)

The rules are consistent (i.e., there is not two actions for the same combinations of conditions)

Cause-effect graphs in black box testingCaptures the relationships between

specific combinations of inputs (causes) and outputs (effects)Deals with specific cases Avoids combinatorial explosionExplore combinations of possible inputs

Causes/effects represented as nodes of a cause effect

graphThe graph also includes a number of

intermediate nodes linking causes and effects

Drawing Cause-Effect Graphs

A B

If A then B (identity)

AC

If (A=true and B=true)then C

B


AC

If (A or B) then C

B

AC

If (not(A AND B)) then C

B


AC

If (not (A OR B))then C

B

A B

If (not A) then B

Constraint Symbols

a

b

at most, one of a and b can be 1 (i.e., a and b cannot be 1 at the same time)

a

b

Exactly one of A and B can be 1

a

bat least one of a, or b must be 1 (i.e., a and b cannot be 0 at the same time)

O

I

E

Example: ATM

•For a simple ATM banking transaction system•Causes (inputs)

• C1: command is credit• C2: command is debit• C3: account number is valid• C4: transaction amount is valid

•Effects (outputs)• E1: print “invalid command”• E2: print “ invalid account number”• E3: print “debit amount not valid”• E4: debit account• E5: credit account

C1

C4

C3

C2

and

and

and

and E3

E2

E1

E5

E4

or

Description of processing nodes used in a Cause-effect graph

Type of processing node description

AND Effect occurs if all input are true (1)

OR Effect occurs if both or one input is true

XOC Effect occurs if one of input is true

Negation Effect occurs if input are false (0)

()

ATM Cause-effect decision table

Cause\effect

R1 R2 R3 R4 R5

C1 0 1 x x 1

C2 0 x 1 1 x

C3 x 0 1 0 1

C4 x x 0 1 1

E1 1 0 0 0 0

E2 0 1 0 0 0

E3 0 0 1 0 0

E4 0 0 0 1 0

E5 0 0 0 0 1

Don’t Care condition

C/E: Print Message problem

The "Print message" is a software that read two characters and, depending of their values, messages must be printed.

The first character must be an "A" or a "B". The second character must be a digit. If the first character is an "A" or "B" and the second character is a digit, the file must be updated.

If the first character is incorrect (not an "A" or "B"), the message X must be printed.

If the second character is incorrect (not a digit), the message Y must be printed.

Step 1: Identify Causes and Effect•Causes:

•1 - first character is "A"

•2 - first character is "B"

•3 - second character is a digit

•Effects:

•70 - the file is updated

•71 - message X is print

•72 - message Y is print

Step 2: Draw the Graph

Step 2: Improved Graph

Exclusive Or (i.e., 1 and 2 cannot be true at same

time)

Step 3: Convert the Graph into Decision table

T1 T2 T3 T4 T5

C1 0 0 1 0 1

C2 0 0 0 1 0

C3 0 1 1 1 0

E1:70 0 0 1 1 0

E2:71 1 1 0 0 0

E3:72 1 0 0 0 1

Steps to create cause-effect graph Study the functional requirements and divide

the requirements into workable pieces Identify causes and effects in the specifications

Causes: distinct input conditions Effects: an output condition or a system transformations.

Assign unique number to each cause and effect Use the semantic content of the spec and

transform it into a Boolean graph Annotate the graph with constrains describing

combinations of causes and/or effects Convert the graph into a limited-entry decision

table Use each column as a test case

Black-box testing

Ie

Input test data

OeOutput test results

System

Inputs causinganomalousbehaviour

Outputs which revealthe presence ofdefects

Ie

Input test data

OeOutput test results

System

Inputs causinganomalousbehaviour

Outputs which revealthe presence ofdefects

Equivalence partitioning

•Black box testing that involves identifying a small set of input values that produces as many different output conditions as possible

•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 design involves• Identifying all partitions satisfying the input values for a product• Identifying all partitions satisfying the expected outputs for a product

•Selecting one member value from each partition to maximize complete coverage

Equivalence partitioning

System

Outputs

Invalid inputs Valid inputs

Guidelines for equivalence classesIf an input condition specifies range,

one valid and two invalid equivalence classes are needed

If an input condition requires a specific value,

then one valid and two invalid equivalence classes are needed

If an input condition specifies a member of a set

one valid and one invalid equivalence class are needed

If an input condition is Boolean, one valid and one invalid class are needed

Example: ATM

•Consider data maintained for ATM•User should be able to access the bank using PC and modem (dialing)

•User needs to provide eight-digit password

•Need to follow a set of typed commands representing various transactions

Data format for phone(xxx-xxx-xxxx)•Software accepts

•Area code: • blank or three-digit

•Prefix: • three-digit number not beginning with 0 or 1

•Suffix: • four digits number

•Password: • eight digit alphanumeric value

•Command: • {“check”, “deposit,” “ bill pay”, “transfer” etc.}

Input conditions for ATM

Input conditions Area code:

Boolean: (the area code may or may not be present) Range: values defined between 200-999 Specific value: no value > 905

Prefix: range : specific value >200

Suffix: Value: four-digit length

Password: Boolean: password may or may not be present value : eight char-string

Command: set containing commands noted previously

Boundary Value Analysis (BVA)• Complements equivalence partitioning• Focuses is on the boundaries of the input

• If input condition specifies a range bounded by a certain values, say, a and b, then test cases should include

• The value for “a” • The value for “b”• The values just above “a”• The values just below “a” • The values just above “b”• The values just below “b”• The nominal value

• If an input condition specifies any number of values, test cases should be exercise

• the minimum and maximum numbers, • the values just above and just below the minimum and

maximum values

Example 2: Equivalence Partitioning (EP)

EP: Process •Identify valid partitions•Identify invalid partitions•Identify output partitions

Input: Valid partitions

•The valid partitions can be•0<=exam mark <=75•0<=course work <=25

Input: Invalid partitions

•The most obvious partitions are•Exam mark > 75•Exam mark < 0•Coursework mark > 25•Coursework nark <0

Exam mark and course work (c/w) mark

Less obvious invalid input EP•Invalid INPUT EP should include

Partitions for the OUTPUTS

•EP for valid OUTPUTS should include

FM

The EP and boundaries

•The EP and boundaries for total mark

Unspecified Outputs

•Three unspecified Outputs errors can be identified •Output = “E” (errors below zero)•Output = “A+” (errors exceeding 100)

•Output = “null” (errors corresponding to blanks)

Total PEs

Input partitions for exams

Input partitions for course works

Output partitions for special cases

Input partitions for invalid data

Output partitions for valid data

Test Cases corresponding to PE exam mark (INPUT)

Test Case 4-6 (coursework)

test case for Invalid inputs

Test cases for outputs:1

Test cases for outputs:2

Test cases for Special output classes:3

Minimal Test cases:1

Minimal Test cases:2

Syntax-Driven testing (SDT): 1•A test case design technique for a component or system in which test case design is based upon the syntax of the input.

•Applicable to •Specification validation written by a certain grammar (BNF)

•Input data validation

Syntax-Driven testing (SDT): 2•Applications•GUI applications •XML/HTML files. •Command-driven software•Scripting languages•Database query languages.

•…

Coverage criteria for SDT•Test generation method• generate test cases such that each production rule is tested at least once (production coverage)

• generate test cases such that each terminal is tested at least once (terminal coverage)

•generate test case such that each string (program sample) is tested (derivation coverage)

More on SDT

•The set of test cases for SDT should include expressions that exercise each production rule, each nonterminal, and all possible input values

•Examples:•9-5+2•5 * 2 + 8/4•…

Parse Tree (PT)

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•Parsing?•It is a process of showing how to take a string of terminals (input) and derives it from start symbol

•Parse Tree (PT)•PT shows how the start symbol of a grammar derives a string in the language

•PT consists of : •the root (start symbol)•Interior nodes (non-terminal)•leaf nodes (terminals)

Step 1: Use a CFG to create the syntax of the input

(example 9-5+2)

59

Exp

TermExp

Term

Exp

Term

2+5-9

•Examples (G s n | B t n)*

BNF Grammars

Using Grammar

Applications of SDT

•Here are some examples•All user interfaces•Operating command processing•All communications interfaces and protocols• Internal interface and protocol (call sequences)

Black Box Testing

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