SOFTWARE ENGINEERING TECHNIQUES

LESSON 24:

Topics Covered An input condition is either a specific numeric value, range of

Functional testing/Black box testing: Equivalence class testing, values, a set of related values, or a boolean condition.
boundary value analysis, Cause effect graphing technique. Equivalence classes can be defined by:
Objectives • If an input condition specifies a range or a specific value,
Upon completion of this Lesson, you should be able to: one valid and two invalid equivalence classes defined.
• Know what is functional testing/black box testing • If an input condition specifies a boolean or a member of a
• Know what are the various testing methods set, one valid and one invalid equivalence classes defined.
• Know what is equivalence class testing and boundary value Test cases for each input domain data item developed and
analysis and the cause effect graphing technique executed.
Black Box Testing This method uses less number of input data compare to
Functional tests examine the observable behavior of software exhaustive testing. However, the data for boundary values are
as evidenced by its outputs, without any reference to internal not considered.
functions. This kind of tests is from the user point of view, This method though reduces significantly the number of input
which means as if the user is testing as in the normal business data to be tested; it does not test the combinations of the input
functions. data.
• Black box tests normally determine the quality of the Boundary Value Analysis
software. It is an advantage to create the quality criteria It is observed that boundary points for any inputs are not
from this point of view from the beginning. tested properly. This leads to many errors. Large number of
• In black box testing, software is subjected to a full range of errors tends to occur at boundaries of the input domain.
inputs and the outputs are verified for its correctness. Here, Boundary Value Analysis (BVA) leads to selection of test cases
the structure of the program is immaterial. that exercise boundary values.
• Black box testing technique can be applied once unit and BVA complements equivalence partitioning i.e. select any
integration testing is completed. element in an equivalence class, select those at the ‘’edge’ of the
• It focuses on functional requirements. class.
• It is compliment to the white box testing. Examples
The main objective of the black box testing is to find: 1. For a range of values bounded by a and b, test (a-1), a,
1. Incorrect or missing functions (a+1), (b-1), b, (b+1).
2. Interface errors 2. If input conditions specify a number of values n, test with
(n-1), n and (n+1) input values.
3. Errors in data structures or external database access
3. Apply 1 and 2 to output conditions (e.g., generate table of
4. Performance errors
minimum and maximum size).
5. Initialization and termination errors.
4. If internal program data structures have boundaries (e.g.,
Some of the techniques used for black box testing are buffer size, table limits), use input data to exercise
discussed below: structures on boundaries.
Equivalence Class Partitioning BVA and Equivalence partitioning both helps in testing the
The main objective of this method is to partitioning the input programs and covers most of the conditions. This method
so that an optimal input data is selected. Steps to be followed does not test the combinations of input conditions.
are:
Cause Effect Graphing Techniques
1. Divide the input domain into classes of data for which test Translation of natural language descriptions of procedures to
cases can be generated. software-based algorithms is error prone.
2. Attempting to uncover classes of errors, if any.
Example: From US Army Corps of Engineers:
3. Identify the both right and wrong input data while Executive Order 10358 provides in the case of an employee
partitioning the data. whose work week varies from the normal Monday through
4. Test the program for all types of data. Friday work week, that Labor Day and Thanksgiving Day each
Based on equivalence classes for input conditions. were to be observed on the next succeeding workday when the
holiday fell on a day outside the employee’s regular basic work
An equivalence class represents a set of valid or invalid states

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 week. Now, when Labor Day, Thanksgiving Day or any of the When outputs of versions differ, each is investigated to
SOFTWARE ENGINEERING TECHNIQUES

new Monday holidays are outside an employee’s basic work- determine if there is a defect.
book, the immediately preceding workday will be his holiday Method does not catch errors in the specification.
when the non-workday on which the holiday falls is the second
non-workday or the non-workday designated as the employee’s Notes
day off in lieu of Saturday. When the non-workday on which
the holiday falls is the first non-workday or the non-workday
designated as the employee’s day off in lieu of Sunday, the
holiday observance is moved to the next succeeding workday.
How do you Test Code, Which Attempts to Implement
this?
Cause-effect graphing attempts to provide a concise representa-
tion of logical combinations and corresponding actions.
1. Causes (input conditions) and effects (actions) are listed for
a module and an identifier is assigned to each.
2. A cause-effect graph developed.
3. Graph converted to a decision table.
4. Decision table rules are converted to test cases.
Simplified Symbology

Fig: Representation of cause-effect nodes

Comparison Testing
In some applications the reliability is critical.
Redundant hardware and software may be used.
For redundant software, use separate teams to develop
independent versions of the software.
Test each version with same test data to ensure all provisional
identical output.
Run all versions in parallel with a real-time comparison of
results.
Even if will only run one version in final system, for some
critical applications can develop independent versions and use
comparison testing or back-to-back testing.

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