Definition of Equivalence Partitioning
Equivalence Partitioning is a black-box testing technique (basic test-design technique) that splits the input domain into classes of data. From this data we can derive test cases.
Test-case 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/Art-Software-Testing-Glenford-Myers/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
Software Engineering. By K K Aggarwal, Yogesh Singh
Pragmatic software testing By Rex Black also has solution
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
Another Good Example on Equivalence Partitioning
Advantages of Equivalence Partitioning
It decreases the scope of extensive testing to a well-defined 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, non-leap 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.
Equivalence Partitioning - Multiple Choice Questions
Also See - More to read on Equivalence Partitioning:
1. shrinik.blogspot.com
2. Test Education
3. csee.usf.edu
4. Test Education
5. Glasnost
6. it.toolbox.com
7. After the Y2K fireworks By Bhuvan Unhelkar
8. Turning Equivalence Class Partitioning Into Child’s Play, an article in stpmag
9. Another worth reading article by Michael Bolton on Domain & Equivalence Partitioning
Related Post:
Boundary Value Analysis