Monday, May 19, 2008

Equivalence Partitioning

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Equivalence partitioning is a software testing technique to minimize number of permutation and combination of input data. In equivalence partitioning, data is selected in such a way that it gives as many different out put as possible with the minimal set of data.
If software behaves in an identical way for a set of value, then the set is termed as equivalence class or a partition. It can be assumed safely that functionality of the software will be same for any data value from the equivalence class or partition. In equivalence partitioning, input data is analyzed and divided into equivalence classes which produces different output.
Now, data from these classes can be representative of all the input values that your software expect. For equivalence classes, it can be assumed that software will behave in exactly same way for any data value from the same partition.
So essentially, there are two steps that you need to follow if you want to use equivalence partitioning in your projects - Identifying equivalence classes or partition Picking one value from each partition for the complete coverage. Main advantage of using this technique is that testing efforts are minimized and at the same time coverage is also ensured. Using this technique, redundancy of test cases is removed by eliminating data which does not produce different output. For example, consider a very simple function for awarding grades to the students. This program follow these guideline to award grades Marks 00 - 39 ------------ Grade D Marks 40 - 59 ------------ Grade C Marks 60 - 70 ------------ Grade B Marks 71 - 100 ------------ Grade A Based on the equivalence partitioning techniques, partitions for this program could be as follows Marks between 0 to 39 - Valid Input Marks between 40 to 59 - Valid Input Marks between 60 to 70 - Valid Input Marks between 71 to 100 - Valid Input Marks less than 0 - Invalid Input Marks more than 100 - Invalid Input Non numeric input - Invalid Input From the example above, it is clear that from infinite possible test cases (Any value between 0 to 100, Infinite values for >100 , < 0 and non numeric) data can be divided into seven distinct classes. Now even if you take only one data value from these partitions, your coverage will be good. Most important part in equivalence partitioning is to identify equivalence classes. Identifying equivalence classes needs close examination of the possible input values. Also, you can not rely on any one technique to ensure your testing is complete. You still need to apply other techniques to find defects. If you have used Equivalence Partitioning in some interesting way, why not share with all?

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