Chapter 2 - White Box Test Techniques

White Box Test Techniques
1 TTA’s Task in
Risk Based Testing
2 White Box Test
Techniques
3 Analytical
Techniques
Software Testing - ISTQB Advance
Technical Test Analyst Exam Preparation
Chapter 2
Neeraj Kumar Singh
4 Dynamic Analysis 5 Reviews
6 Test Tools &
Automation

Contents
2.1 Introduction
2.2 Statement Testing
2.3 Decision Testing
2.4 Modified Condition/Decision Coverage
(MC/DC) Testing
2.5 Multiple Condition Testing
2.6 Basis Path Testing
2.7 API Testing
2.8 Selecting a White-box Test Technique
Neeraj Kumar Singh

Introduction
Each specific technique enables test cases to be derived systematically and focuses on a particular aspect of the
structure to be considered. The techniques provide coverage criteria which have to be measured and associated
with an objective defined by each project or organization.
Achieving full coverage does not mean that the entire set of tests is complete, but rather that the technique being
used no longer suggests any useful tests for the structure under consideration.
The following techniques are considered in this syllabus:
 Statement testing
 Decision testing
 Modified Condition/Decision Coverage (MC/DC) testing
 Multiple Condition testing
 Basis Path testing
 API testing
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Statement Testing
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True
False?
Read A
Read B
If A>B then
Print “A is Bigger”
Else
Print “B is Bigger”
End If
Statement Testing or Coverage is a measure of the number of
executable statements in the source code exercised by tests.
Start
End
Branch
Nodes
A,B
A>B
A
B
End If

Statement Testing
True
False?
Read A
Read B
If A>B then
Else
End If
Start
End
A Path is the executable path which reaches the end of
the code starting from the start point.
2
1
A,B
A>B
A
B
End If

Example
Statement Testing
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T
IF sufficient water THEN
Boil water
Add tea
Show message “milk?”
IF milk = yes THEN
Show message “low fat?”
IF low fat = yes THEN
Add low fat milk
ELSE
Add normal milk
ENDIF
ENDIF
Show message “sugar?”
IF sugar = yes THEN
Add sugar
ENDIF
Stir
Wait 3 minutes
Show message “please take your tea”
ELSE
Show message “please fill up water”
ENDIF
Sufficient
Water
Boil
Water
Add
Tea
Milk?
Milk=Yes
Low
Fat?
Low Fat
= Yes
Low fat
Milk
Normal
Milk
End If
Sugar?
Sugar
=Yes
End If
Add
Sugar?
End If
Please fill
up water
Stir, wait
Please take your tea.
End If
F
F
T
T
F
F
T

Decision Testing
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True
False?
Read A
Read B
If A>B then
Else
End If
Decision Testing or Coverage is a measure of the number of executable
decisions in the source code exercised by tests.
Start
End
Branch/
Decisions
Nodes/
Statements
A,B
A>B
A
B
End If

Decision Testing
True
False?
Read A
Read B
If A>B then
Else
End If
Start
End
A Path is the executable path which reaches the end of
the code starting from the start point.
2
1
A,B
A>B
A
B
End If

Example
Decision Testing
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TStatement P
IF A THEN
IF B THEN
Statement Q
ELSE
Statement R
ENDIF
ELSE
Statement S
IF C THEN
Statement T
ELSE
Statement U
ENDIF
ENDIF
Statement V
How many test cases would you design to achieve 100%
decision coverage?
A
STMT P
END IF
F
F F
B
STMT Q
T
STMT R
STMT S
C
T
STMT T
STMT U
END IF
END IF
STMT V
Min TC for 100% DC = 4
#TIP – No of If +1

Modified Condition/Decision Coverage(MC/DC)
Compared to Decision testing, which considers the entire decision as a whole and evaluates the TRUE and FALSE
outcomes in separate test cases, MC/DC testing considers how a decision is made when it includes multiple
conditions
Each decision predicate is made up of one or more simple atomic conditions, each of which evaluates to a discrete
Boolean value. These are logically combined to determine the final outcome of the decision. This technique checks
that each of the atomic conditions independently and correctly affects the outcome of the overall decision.
This technique provides a stronger level of coverage than statement and decision coverage when there are
decisions containing multiple conditions.
Assuming N unique, independent atomic conditions, MC/DC can usually be achieved with N+1 unique test cases.
MC/DC requires pairs of test cases that show a single atomic condition can independently affect the result of a
decision.
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Tests A B C Outcome
1 T T T T
2 T T F T
3 T F T T
4 T F F F
5 F T T F
6 F T F F
7 F F T F
8 F F F F
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(A && (B | C))
(A AND (B OR C))
Min TC for 100% MC/DC Coverage is N+1
Where N is no of conditions

Tests A B C Outcome
1 T T T T
2 T T F T
3 T F T T
4 T F F F
5 F T T F
6 F T F F
7 F F T F
8 F F F F
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(A && (B | C))
(A AND (B OR C))

Tests A B C Outcome
1 T T T T
2 T T F T
3 T F T T
4 T F F F
5 F T T F
6 F T F F
7 F F T F
8 F F F F
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(A && (B | C))
(A AND (B OR C))
A = {1,5} {2,6} {3,7}
B = {2,4}
C = {3,4}

Tests A B C Outcome
1 T T T T
2 T T F T
3 T F T T
4 T F F F
5 F T T F
6 F T F F
7 F F T F
8 F F F F
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(A && (B | C))
(A AND (B OR C))
Min TC for 100% MC/DC Coverage is N+1
A = {1,5} {2,6} {3,7}
B = {2,4}
C = {3,4}
TC = {2,3,4,6}

Multiple Condition Testing
In rare instances, it might be required to test all possible combinations of atomic conditions that a decision may
contain. This exhaustive level of testing is called multiple condition testing.
The number of required tests is dependent on the number of atomic conditions in the decision statement and can
be determined by calculating 2N where N is the number of uncoupled atomic conditions.
Coverage is measured as the number of unique condition combinations executed by the tests divided by the total
number of condition combinations in the test object, normally expressed as a percentage.
The number of test cases can be derived directly from a truth table containing all of the atomic conditions, this
level of coverage can easily be determined. However, the sheer number of test cases required makes MC/DC
coverage more feasible for most situations.
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Multiple Condition Testing
Tests A B C Outcome
1 T T T T
2 T T F T
3 T F T T
4 T F F F
5 F T T F
6 F T F F
7 F F T F
8 F F F F
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(A && (B | C))
(A AND (B OR C))
Min TC for 100% MCT Coverage is 2N

Basis Path Testing
Path testing in general consists of identifying paths through the code and then creating tests to cover them.
Conceptually, it would be useful to test every unique path through the system. In any non-trivial system, however,
the number of test cases could become excessively large due to the nature of looping structures.
The technique is applied by the following steps:
1. Create a control flow graph for a given specification item (e.g., code or functional design specification). Note
that this may also be the first step in performing control flow analysis.
2. Select a baseline path through the code (not an exception path). This baseline path should be the most
important path to test – risk could be used to make this judgment.
3. Generate the second path by changing the outcome of the first decision on the path, while keeping the
maximum number of decision outcomes the same as the baseline path.
4. Generate the third path by again starting with the baseline path and changing the outcome of the second
decision on the path. When multiway decisions are encountered (e.g., a case statement), each outcome of the
decision should be exercised before moving on to the next decision.
5. Generate further paths by changing each of the outcomes on the baseline path. When new decisions are
encountered, the most important outcome should be followed first.
6. Once all the decision outcomes on the baseline path have been covered, apply the same approach to
subsequent paths until all the decision outcomes in the specification item have been exercised.
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Basis Path Testing
Tests Paper Pen Pencil Outcome
1 T T T T
2 T T F T
3 T F T T
4 T F F F
5 F T T F
6 F T F F
7 F F T F
8 F F F F
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(A && (B | C)) = Write
(Paper AND (Pen OR Pencil))

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Basis Path Testing
TStatement P
IF A THEN
IF B THEN
Statement Q
ELSE
Statement R
ENDIF
ELSE
Statement S
IF C THEN
Statement T
ELSE
Statement U
ENDIF
ENDIF
Statement V
A
STMT P
END IF
F
F F
B
STMT Q
T
STMT R
STMT S
C
T
STMT T
STMT U
END IF
END IF
STMT V

API Testing
An Application Programming Interface (API) is code which enables communication between different processes,
programs and/or systems. APIs are often utilized in a client/server relationship where one process supplies some
kind of functionality to other processes.
API Testing is a type of testing rather than a technique. In certain respects, API testing is quite similar to testing a
graphical user interface (GUI). The focus is on the evaluation of input values and returned data.
Negative testing is often crucial when dealing with APIs. Programmers who use APIs to access services external to
their own code may try to use API interfaces in ways for which they were not intended. That means that robust
error handling is essential to avoid incorrect operation.
Combinatorial testing of many different interfaces may be required because APIs are often used in conjunction
with other APIs, and because a single interface may contain several parameters, where values of these may be
combined in many ways.
APIs frequently are loosely coupled, resulting in the very real possibility of lost transactions or timing glitches. This
necessitates thorough testing of the recovery and retry mechanisms. An organization that provides an API interface
must ensure that all services have a very high availability; this often requires strict reliability testing by the API
publisher as well as infrastructure support.
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API Testing
Applicability
API testing is becoming more important for testing systems of systems as the individual systems become distributed or
use remote processing as a way of off-loading some work to other processors. Examples include:
 Operating systems calls
 Service-oriented architectures (SOA)
 Remote procedure calls (RPC)
 Web services
Software containerization results in the division of a software program into several containers which communicate
with each other using mechanisms such as those listed above. API testing should also target these interfaces.
Limitations/Difficulties
Testing an API directly usually requires a Technical Test Analyst to use specialized tools. Because there is typically no
direct graphical interface associated with an API, tools may be required to setup the initial environment, marshal the
data, invoke the API, and determine the result.
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Selecting a White-box Test Technique
The context of the system under test will have an impact on its product risk and criticality levels ( see below).
These factors influence the required coverage metric (and hence the white-box test technique to use) and the
depth of coverage to be achieved. In general, the more critical the system and the higher the product risk level,
the more rigorous the coverage requirements and the higher the need for time and resources to achieve the
desired coverage.
Sometimes the required coverage metric may be derived from applicable standards that apply to the software
system. For example, if the software were to be used in an airborne environment, it may be required to conform
to standard DO-178C (in Europe, ED-12C.)
This standard contains the following five failure conditions:
A. Catastrophic: failure may cause lack of critical function needed to safely fly or land the plane
B. Hazardous: failure may have a large negative impact on safety or performance efficiency
C. Major: failure is significant, but less serious than A or B
D. Minor: failure is noticeable, but with less impact than C
E. No effect: failure has no impact on safety
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Selecting a White-box Test Technique
If the software system is categorized as level A, it must be tested to 100% MC/DC coverage. If it is level B, it must
be tested to 100% decision level coverage and MC/DC is optional. Level C requires 100% statement coverage at a
minimum.
Likewise, [IEC61508] is an international standard for the functional safety of programmable, electronic, safety-
related systems. This standard has been adapted in many different areas, including automotive, rail,
manufacturing, nuclear power plants, and machinery. Criticality is defined using a scale of Safety Integrity Levels
(SIL) where SIL1 is the least critical and SIL4 the most critical. The standard gives recommendations for test
coverage, as shown in the following table (note that the exact definitions for each SIL and for the meaning of
“recommended” and “highly recommended” is defined in the standard).
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Sample Questions Pattern
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Source : www.istqb.org
Chapter 2 Questions
Distribution
K-Level Number of Questions per
LO(Group)
Summary
TTA-2.2 K3 1
There is a total of questions required
for chapter 2
K3 = 6
K4 = 2
TTA-2.3 K3 1
TTA-2.4 K3 1
TTA-2.5 K3 1
TTA-2.6 K3 1
TTA-2.7 K3 1
TTA-2.8 K4 2

Sample Questions
1. You are testing a photo-enforcement system for traffic control in an intersection. It has been determined that a photo
should be taken if the signal light is red (RED) or the car is speeding (SPEED) and if the front wheels of the car are over
the line marking the beginning of the intersection (WHEELS).
Consider these sets of test values:
Assume the logic in the code is as follows:
IF ((RED OR SPEED) AND WHEELS) THEN
TAKE THE PHOTO
ELSE
DO NOT TAKE THE PHOTO
Given this information, which sets of values provides the minimum tests to achieve 100% modified condition/decision
coverage?
Select ONE option.
Answer Set
a. 1, 3, and 8.
b. 2 and 8.
c. 3, 4, 5, and 7.
d. 1, 5, 7, and 8.
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1. RED + SPEED + WHEELS
2. RED + SPEED + not WHEELS
3. RED + not SPEED + WHEELS
4. RED + not SPEED + not WHEELS
5. not RED + SPEED + WHEELS
6. not RED + SPEED + not WHEELS
7. not RED + not SPEED + WHEELS
8. not RED + not SPEED + not WHEELS

Sample Questions
TAKE THE PHOTO
ELSE
Given this information, which sets of values provide the minimum tests to achieve 100% multiple condition coverage?
Select ONE option.
Answer Set
a. All the sets are needed.
b. 3, 4, 5, and 7.
c. 1, 3, and 8.
d. 1, 5, 7, and 8.
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Sample Questions
TAKE THE PHOTO
ELSE
Given this information, which sets of values provide the minimum tests to achieve full coverage of basis paths?
Select ONE option.
Answer Set
a. 3, 4, 5, 7
b. 2, 3
c. 1, 3, 8
d. 1
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Sample Questions
4. Which of the following types of defects are targeted by API testing?
Select TWO options.
Answer Set
a. Loss of transactions.
b. Non-conformance to coding standards.
c. Incorrect data handling.
d. Installation defects.
e. GUI faults.
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Sample Questions
5. You are advising the developers in an agile team on the appropriate test coverage to be achieved in the next
sprint. Three business-critical user stories are on the sprint backlog. Each user story requires that several
sequential actions are performed with some simple error handling routines. Which is the level of test coverage
you would expect to be achieved in the testing of the user stories??
Select ONE option.
Answer Set
a. Decision coverage + Modified Condition/Decision coverage.
b. Decision coverage + Statement coverage.
c. Modified Condition/Decision coverage.
d. Multiple Condition coverage.
Neeraj Kumar Singh

Chapter 2 - White Box Test Techniques

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