Welcome to this post on Orthogonal Array Testing in software engineering. Orthogonal array testing is black box testing. When you have a large number of input combinations, orthogonal array testing gives very few test cases.

What is Orthogonal Array? It is a table. The columns (a.k.a. factors) represent the independent variables. The rows (a.k.a. experiments or runs) represent the variables' combinations. The orthogonal array testing example below is for a web page with three sections - TOP, LEFT and RIGHT. Note that the orthogonal array has only 4 test cases to run for 8 input combinations.

What is Orthogonal Array Testing? The Orthogonal Array Technique has the following steps:

- Identify the independent variables. Put them as column headers in the table.
- For each independent variable, identify the number of possible values.
- Search an Orthogonal Array with the smallest number of rows in orthogonal array design of experiments. I have explained this step here.
- Put the independent variable values in the Orthogonal Array cells. If any cells are still blank, repeat the values in them.
- Test each row in the table.

In the example below, there are 3 independent variables (put as column headers). Variable A has 2 possible values, A1 and A2. Variable B has 3 possible values, B1, B2 and B3. Variable C has 3 possible values, C1, C2 and C3. The input combinations are therefore 2 * 3 * 3, which is 18. The smallest number of rows can be found in this orthogonal array. Using the above orthogonal array technique, the table should look like below. Instead of testing 18 input combinations, orthogonal array gives only 9 test cases to run.

*Note: 1) Since variable A has only 2 values, they are used to complete the first column.2) Since there are only 3 variables, the 4th column is not used. *

Want to learn the above Orthogonal Array Testing examples in detail? Please view my Orthogonal Array Testing tutorial.

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