In the ever-evolving world of software development, where time is of the essence and quality is paramount, finding efficient and effective testing techniques is crucial. By significantly reducing the number of test cases required, pairwise testing saves time, effort, and resources without compromising the thoroughness of the testing process.

In software development, there are usually many possible combinations of input values, and it is not possible to within the time-to-market constraints and strict project deadlines. Pairwise testing is a technique used in software testing to ensure that the most efficient and effective testing is performed. Also known as all-pairs testing, it is a form of combinatorial testing that aims to cover all possible combinations of input values with the minimum number of test cases. Pairwise testing helps software testers identify defects or errors that might be missed during regular testing. It ensures that every combination of inputs is tested at least once by using a systematic and efficient approach to create the minimum number of test cases.

Increased Efficiency: Pairwise testing can significantly reduce the number of test cases required to achieve comprehensive coverage. By testing all pairs of input values, it ensures that defects are detected with minimal testing effort.

Better Coverage: Pairwise testing covers more scenarios than traditional testing methods. By testing all possible pairs of input values, it ensures that all possible combinations of input values are covered, thereby increasing the likelihood of detecting defects.

Improved Quality: Pairwise testing can improve the quality of software by identifying defects that might be missed during regular testing. By identifying and fixing defects early in the development cycle, software quality can be improved, and the overall cost of development reduced.

Reduced Testing Time: Pairwise testing can save time and reduce the overall cost of testing. By selecting a subset of input combinations, it reduces the number of test cases required, thereby reducing the time and resources required for testing.

Pairwise testing involves the following steps:

• Identify the input parameters: The first step is to identify the input parameters that need to be tested.
• Define the values for each input parameter: The next step is to define the values that each input parameter can take.
• Generate pairwise combinations: Using a pairwise testing tool, all possible pairs of input values are generated. Each pair represents a unique combination of input values that needs to be tested.
• Execute the test cases: The test cases are then executed, and any defects or errors are recorded.

Suppose you are testing a software application for a flight booking system. The system allows users to search and book flights based on various parameters such as departure city, destination, travel class, and stop options. Let’s list down the variables involved:

1. Departure City
   1. New York
   2. Los Angeles
   3. Chicago
   4. Miami
2. Destination
   1. London
   2. Paris
   3. Tokyo
   4. Sydney
3. Travel Class
   1. Economy
   2. Business
   3. First
4. Stop Options
   1. Direct
   2. 1 Stop
   3. 2 Stops

When we arrange the variables and values involved, it looks something like this:

If you want to test all possible valid combinations:
= 4 x 4 x 3 x 3
= 144 Valid test case combinations ☹️. 

There is also an infinite number of invalid combinations.

Let’s now reconsider this example according to the pairwise testing technique.

In this technique, the number of test cases is determined by multiplying the highest two input values. According to this information, the number of test scenarios in our example would be 16.

Number of test cases = 4 x 4

Let’s start filling in the table column by column. Initially, the table should look something like this. The four values of Departure City (the variable having the highest number of values) should be written four times each (four is the number of values of the next highest variable i.e., Destination).

The destination column has four values. That’s how many times we need to insert the values of the first column, departure city.

For each set of values in column 1, we put each value in column 2. Repeat the same for column 3.

We will repeat the same steps for column 4.

Using the pairwise technique, the following test scenarios will be sufficient for this test. Some existing tools can be used to create this table.

In the above example, all possible pairs of input values have been covered with only 16 test cases. This looks much better!

Pairwise testing, generally covers between %70 – 85 of the total tests. If input values and their correlation are not properly done, test results may not be reliable, so it is important to ensure that the most valid combinations are tested. The pairwise testing covers the most important parts, but it is necessary to remember that there is a risk for the parts that are not included in the coverage.

There are many pairwise testing tools available that can help you generate the most efficient and effective set of test cases. Here are some popular pairwise testing tools:

1. PICT: PICT (Pairwise Independent Combinatorial Tool) is a free and open source pairwise testing tool that can generate test cases based on a set of input parameters and their respective values.
2. AllPairs: AllPairs is another free pairwise testing tool that can generate test cases based on input parameters and values.
3. Hexawise: Hexawise is a commercial pairwise testing tool that can generate test cases based on a range of input parameters and values. Hexawise offers a range of customization options, including test prioritization, constraint testing, and test traceability.
4. CTE-XL: CTE-XL is a pairwise testing tool that is available as a Microsoft Excel add-in. CTE-XL can generate test cases based on input parameters and values and provides a range of customization options, including the ability to define test constraints and test data dependencies.
5. TestCover: TestCover is a commercial pairwise testing tool that can generate test cases based on a range of input parameters and values. TestCover offers a range of customization options, including test prioritization, test data filtering, and test traceability.

Pairwise testing is a powerful technique that allows software developers and testers to enhance software quality while minimizing effort. Selecting representative test cases that cover all possible combinations, significantly reduces the number of test cases required while maintaining a high degree of coverage.

It aligns well with Agile development methodologies, where time constraints and rapid iterations are common. Its ability to achieve high coverage with minimal effort makes it an ideal choice for Agile teams seeking to balance efficiency and quality.

Happy testing! 🙂