Black Box Testing

Adam Hendra Brata

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Agenda

Black Box Testing– Techniques

Cause Effect Graph

Decision Table

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Black Box Testing TechniquesCause Effect Graph

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Cause Effect Graph

One weakness of boundary-value analysis and

equivalence partitioning is that they do not explore

combinations of input circumstances

The testing of input combinations is not a simple task

because even if you equivalence-partition the input

conditions, the number of combinations usually is

astronomical

– If you have no systematic way of selecting a subset of input

conditions, you’ll probably select an arbitrary subset of

conditions, which could lead to an ineffective test.

A cause-effect graph is a formal language into which a

natural language specification is translated.

– The graph actually is a digital logic circuit (a combinatorial

logic network)

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Cause Effect Graph

Cause-Effect Graph graphically shows the connection

between a given outcome and all issues that manipulate

the outcome

Cause Effect Graph is also known as Ishikawa diagram

because of the way it looks, invented by Kaoru Ishikawa

or fish bone diagram

It is a testing technique that aids in choosing test cases

that logically relate Causes (inputs) to Effects (outputs) to

produce test cases.

– A “Cause” stands for a separate input condition that fetches

about an internal change in the system.

– An “Effect” represents an output condition, a system

transformation or a state resulting from a combination of

causes.

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Cause Effect Graph

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Cause Effect Graph

Circumstances under which Cause-Effect Diagram

used

– To Identify the possible root causes, the reasons for a

specific effect, problem, or outcome.

– To Relate the interactions and connections of the system

among the factors affecting a particular process or effect.

– To Analyze the existing problems so that corrective action or

the right decision can be taken at the earliest.

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Cause Effect Graph

Benefits

– It Helps us to determine the root causes of a problem or

quality using a structured approach.

– It Uses an orderly, easy-to-read format to diagram cause-

and-effect relationships.

– It Indicates possible causes of variation in a process.

– It Identifies areas, where data should be collected for further

study.

– It Encourages team participation and utilizes the team

knowledge of the process.

– It Increases knowledge of the process by helping everyone

to learn more about the factors at work and how they relate.

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Cause Effect Graph Notation : Basic

• Just assume that each node having

the value 0 or 1 where 0 shows the

‘absent state’ and 1 shows the

‘present state’.

• The identity function states when

c1 = 1, e1 = 1 or we can say if c0 =

0 and e0 = 0.

• The NOT function states that, if C1

= 1, e1= 0 and vice-versa.

• Likewise, OR function states that, if

C1 or C2 or C3 = 1, e1 = 1 else e1 =

0.

• The AND function states that, if both

C1 and C2 = 1, e1 = 1, else e1 = 0.

The AND and OR functions are

permitted to have any number of

inputs.

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Cause Effect Graph

• Draw the graph using the basic notation could

contain an impossible combination of causes

• Suppose, it is impossible for both causes 1 and 2 to be

set to 1 simultaneously.

• In most programs, certain combinations of causes are

impossible because of syntactic or environmental

considerations

• To account for these problem, the constraint notation

can be used

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Cause Effect Graph Notation : Constraint

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Cause Effect Graph Notation : Constraint

• The E constraint states that it must always be true that, at

most, one of a and b can be 1 (a and b cannot be 1

simultaneously)

• The I constraint states that at least one of a,b, and c must

always be 1 (a,and b cannot be 0 simultaneously)

• The O constraint states that one, and only one, of a and b

must be 1

• The R constraint states that for a to be 1, b must be 1

(i.e., it is impossible for a to be 1 and b to be 0)

• The M constraint states that if effect a is 1, effect b is

forced to 0

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Cause Effect Graph

Steps for drawing cause-Effect Diagram:

– Step 1 : Identify and Define the Effect

– Step 2 : Fill in the Effect Box and Draw the Spine

– Step 3: Identify the main causes contributing to the effect

being studied

– Step 4 : For each major branch, identify other specific

factors which may be the causes of the EFFECT

– Step 5 : Categorize relative causes and provide detailed

levels of causes

– Step 6 : Convert cause-effect graph into a decision table

– Step 7 : Convert decision table rules to test cases, each

column of the decision table represents a test case

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Cause Effect Graph Example

Consider this specification

– The character in column 1 must be an “A” or a “B.” The

character in column 2 must be a digit. In this situation, the

file update is made. If the first character is incorrect,

message X12 is issued. If the second character is not a

digit, message X13 is issued

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Cause Effect Graph Example

Causes

– 1 — character in column 1 is “A”

– 2 — character in column 1 is “B”

– 3 — character in column 2 is a digit

Effect

– 70 — update made

– 71 — message X12 is issued

– 72 — message X13 is issued

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Cause Effect Graph Example

Cause Effect Graph

Notes

– Notice the intermediate node 11 that was created.

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Cause Effect Graph Example

The equivalence logic diagram

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Cause Effect Graph Example

Consider this further specification

– Although the previous graph represents the specification, it

does contain an impossible combination of causes it is

impossible for both causes 1 and 2 to be set to 1

simultaneously

– In most programs, certain combinations of causes are

impossible because of syntactic or environmental

considerations (a character cannot be an “A” and a “B”

simultaneously)

– To account for these, the E constraint states that it must

always be true that, at most, one of a and b can be 1 (a and

b cannot be 1 simultaneously

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Cause Effect Graph Example

Cause Effect Graph with exclusive constraint

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Black Box Testing TechniquesDecision Table

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Decision Table

A decision table is a good way to deal with different

combination inputs with their associated outputs and also

called cause-effect table

Reason to call cause-effect table is an associated logical

diagramming technique called ’cause-effect graphing that

is basically use to derive the decision table

Decision tables are very much helpful in test design

technique

– It helps testers to search the effects of combinations of

different inputs and other software states that must correctly

implement business rules

– Also, provides a regular way of stating complex business

rules, that’s helpful for developers as well as for testers

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Decision Table Example

Based on the previous Cause Effect Graph Example

The tables columns represent the possible generated test

cases and the rows represent all of the cause effect graph’s

nodes

Action TC1 TC1 TC1 TC1 TC1 TC1

1 1 0 0 0 1 0

2 0 1 0 0 0 1

3 1 1 0 1 0 0

70 1 1 0 0 0 0

71 0 0 1 1 0 0

72 0 0 0 0 1 1

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Decision Table Example

Sample generated test cases

TC1 and TC2 are generated from the previous decision table

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Advantages of Decision Table

Advantages

– Any complex business flow can be easily converted into the

test scenarios & test cases using this technique

– Such type of table are work iteratively, means the table

created at the first iteration is used as input table for next

tables. Such iteration can be carried out only if the initial

table is unsatisfactory

– Simple to understand and everyone can use this method

design the test scenarios & test cases

– It provide complete coverage of test cases which help to

reduce the rework on writing test scenarios & test cases

– These tables guarantee that we consider every possible

combination of condition values. This is known as its

“completeness property”

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Thank You