Definition of Equivalence Partitioning
Equivalence Partitioning is a blackbox testing technique (basic testdesign technique) that splits the input domain into classes of data. From this data we can derive test cases.
Testcase design with the help of equivalence partitioning technique has two steps:
1) Identifying the equivalence classes.
2) Defining the test cases.
Example 1 of Equivalence Partitioning
Problem:
The program reads three integer values from an input dialog. The three values represent the lengths of the sides of a triangle. The program displays a message that states whether the triangle is scalene, isosceles, or equilateral. Remember that a scalene triangle is one where no two sides are equal, whereas an isosceles triangle has two equal sides, and an equilateral triangle has three sides of equal length. Moreover, the angles opposite the equal sides in an isosceles triangle also are equal (it also follows that the sides opposite equal angles in a triangle are equal), and all angles in an equilateral triangle are equal.
(Source: http://www.amazon.com/ArtSoftwareTestingGlenfordMyers/dp/0471043281)
Solution:
As seen in the definition above we have to identify equivalence classes and define test cases based on those classes.
Equivalence Classes for the triangle problem
Test Cases (Valid)
for Equilateral Triangle
Test Case #

Side1

Side2

Side3

Expected Output

1

5

5

5

Equilateral

Test Cases (Valid) for Isosceles Triangle
Test Case #

Side1

Side2

Side3

Expected Output

1

2

2

3

Isosceles

2

2

3

2

Isosceles

3

3

2

2

Isosceles

Test Cases (Valid) for Scalene Triangle
Test Case #

Side1

Side2

Side3

Expected Output

1

3

4

6

Scalene

2

3

6

4

Scalene

3

4

3

6

Scalene

Test Cases (Invalid) Not a Triangle
Test Case #

Side1

Side2

Side3

Expected Output

1

3

1

2

Not a
triangle

2

2

3

1

Not a
triangle

3

1

2

4

Not a
triangle

More solutions to the triangle problem
Solution 1
Solution 2
Solution 3
Solution 4
Example 2 of Equivalence Partitioning
The specifications for a application software system for authenticating expenses claim for motel accomodation for one night includes the following requirements:
Upper limit is $100 for accomodation expenses claims.
Any claims above $100 should be rejected and should cause an error message to be displayed.
Expense amounts should be greater than $0 and an error message should be displayed otherwise.
Designing test
cases
Test case ID

Motel Charge

Equivalence class

Expected output

1

65

0 <
Motel Charge<=100

OK

2

24

Motel
Charge <=0

Error
message

3

110

Motel
Charge > 100

Error
message

Another Example of Equivalence Partition
Advantages of Equivalence Partitioning
It decreases the scope of extensive testing to a welldefined set of test procedures i.e. it reduces the number of required test cases by identifying classes of data. This in a way also helps to reduce redundant test cases.
Drawbacks of Equivalence Partitioning
The resultant test procedures do not include other types of tests that may have a high likelihood of finding an error. e.g. suppose for some problem we might need to define equivalence classes for infinite number of days.
first day of month
middle day of month
last day of month
last day of year
28th of February, nonleap year
28th of February, leap year
29th of February, leap year
In this way we surely bring down the number of test cases but equivalence partitioning may not check unexpected input as 32nd of November.
2 comments:
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