Equivalence Partitioning: What is it?

Equivalence partitioning or EP is a method for testing software programs. People also call it the equivalence class partitioning (ECP). In this technique, the data fed into the software that will undergo testing is divided into partitions of equal sizes. From each separation of data, one test case is needed. The different test cases must test the classes of the software continuously. As the aim of the test is to find faults, then a successful test case is the one that does find a defect.

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In this principle, test cases are designed to cover each partition at least once. This technique tries to define the test cases that uncover classes of errors. therefore, reducing the total number of test cases that must be developed. An advantage of this approach is a reduction in the time required for testing software due to a lesser amount of test cases.

How does it work?

It divides the input domain of a program into different classes of data from which you can usually obtain the test cases. The theory says we only need to do one test case for each “class” of input data. The intent is to define a representative or “power” test case that uncovers a class of errors, thereby reducing the total number of test cases that must be developed.

Also, equivalence partitioning is a black-box or specification-based technique. You may use this at any level of a test as well. It is also often an excellent technique to use at first. The idea with this technique is to divide a set of test conditions into groups or sets that can be considered the same. Moreover, equivalence partitions are also equivalence classes – the two terms mean precisely the same thing.

In the equivalence-partitioning technique, we will need to test only one condition from each partition. This is because we are assuming that all the requirements in one partition will be treated in the same way by the software. If one condition in a partition works, we believe all of the terms in that partition will work. Hence, there is little point in testing any of these others. Similarly, if one of the terms in a partition does not work, then we assume that none of the conditions in that partition will work, so again, there is little point in testing any more in that partition.

Importance of doing both boundary value and equivalence partitioning

Technically, because every boundary is in some division. If you have only done the boundary value analysis, then you would also have to test every equivalence partition. However, this kind of approach may cause problems if that value fails.

Also, by testing only boundaries, we would probably not give the users much confidence. As we are using extreme values rather than typical values. The limits may be more difficult and, therefore, more costly to set up as well.


The benefit of ‘Equivalence Partitioning’ is, it allows the testers to reduce the number of test cases. Also, it reduces the testing time of software because of the fewer amount of test cases. If you have additional points, use the comment box below.

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