Equivalence Partitioning

Overview

Equivalence partitioning, also known as equivalence class partitioning (ECP), is a software testing technique used to reduce the number of test cases that need to be developed while still ensuring the adequate coverage of the test suite. It is a method that divides the input data of a software unit into partitions of equivalent data from which test cases can be derived. In principle, test cases are designed to cover each partition at least once. This technique tries to define test case that uncovers classes of errors, thereby reducing the total number of test cases that must be developed.

Concept

The concept of equivalence partitioning lies in the observation that there are certain sets of input data that are expected to be processed in the same way by the software unit under test. These sets are known as equivalence classes. The input data within an equivalence class is assumed to be equivalent, and it is expected that they all will be processed in the same way. If a test case uncovers an error for a member of an equivalence class, it is assumed that all the other members of the class will also uncover the same error. Therefore, it is sufficient to select one test case out of each equivalence class for testing.

Partitioning

The process of partitioning involves dividing the input data into several equivalence classes. The equivalence classes can be defined based on the following criteria:

- Valid Equivalence Classes: These are classes that are within the valid input domain of the software unit. They represent values that the software is expected to handle and process correctly.

- Invalid Equivalence Classes: These are classes that are outside the valid input domain of the software unit. They represent values that the software is not expected to handle. Testing with these values is done to ensure that the software handles unexpected or invalid input gracefully.

Test Case Design

Once the equivalence classes have been identified, the next step is to design test cases. One test case for each equivalence class is usually sufficient. If an equivalence class represents a range of values, a test case that represents a typical value or an edge value from the class is selected.

Benefits

Equivalence partitioning has several benefits:

- It helps to reduce the number of test cases to a manageable level while still maintaining reasonable test coverage.

- It helps to uncover classes of errors that might otherwise be overlooked in the rush to cover as many different test cases as possible.

- It helps to make the testing process more systematic and efficient.

- It can be used at any level of testing and is not restricted to any particular type of testing or phase of the software development lifecycle.

Limitations

While equivalence partitioning is a powerful and efficient testing technique, it has some limitations:

- It is based on the assumption that all the members of an equivalence class are truly equivalent, which may not always be the case.

- It may not be effective in uncovering errors that are specific to certain input data within an equivalence class.

- It requires a good understanding of the software unit's specifications and the input domain, which may not always be available or easy to understand.

Practical Example

Consider a software application that accepts an integer value between 1 and 100. The valid equivalence class will be any number between 1 and 100. The invalid equivalence classes will be any number below 1 and any number above 100. One test case for each of these classes would be sufficient to test the application.