Combinatorial Testing | What it is, How to Perform & Tools

If you are a software tester, you can perform various testing methods to make sure that your software application is developed with good quality. However, if you have a software application with a high complexity and a lot of input possibilities, you may have a lot of testing to do. It would take a long time to design and execute all the test scenarios. Also, there is a high chance of missing some of the test scenarios even if you try your best to give 100% test coverage with a large number of test cases. This is the situation in which you need help from the test technique called combinatorial testing. 

With this article, we are going to learn what combinatorial testing is, how to write a combinatorial test case, and what tools we can use to perform combinatorial testing.

What is Combinatorial Testing in Software Testing?

Combinatorial testing is a testing method that uses multiple combinations of input parameters to perform testing for a software application. The main goal of combinatorial testing is to make sure that the software product can handle different combinations of test data as input parameters and configuration options. 

Testers use combinatorial testing based on the idea that defects in a software application can occur by specific combinations of input parameters rather than by isolated inputs. By focusing on the input combinations like that, the testers can provide effective test coverage while reducing the number of test cases written. 

What Are the Benefits of Combinatorial Testing?

Combinatorial testing has many advantages when it comes to ensuring the quality of a software product. That is why testers choose combinatorial testing over normal software testing methods when testing complicated software applications. Let us get to know some of the benefits of combinatorial testing.

• Covers a broad range of input combinations using a minimum number of test cases.
• Increases test coverage compared to normal component testing since it always considers multiple input combinations.
• Helps to detect bugs, defects, vulnerabilities, and unexpected outputs that might not be detected during the usual component and regression testing phases.
• Reduces testing effort, cost, and time. (Since combinatorial tests use fewer test cases to cover a wide scope of testing.)
• Identifies issues at the earliest while allowing the team to address and fix those earlier in the software development life cycle.
• Optimizes the testing process by removing unwanted test cases while ensuring that the cost and effort are not wasted on repeating the same test scenarios again and again.
• Helps to test complex software applications with a large number of parameters, settings, and options.
• Reduces the risk of critical defects going unnoticed, which can occur only when handling specific input combinations.

Combinatorial Test Case

A combinatorial test case is very different from a normal test case, and it is a specific test scenario that is created using combinatorial test techniques. That is designed to cover various combinations of input parameters of a software application. Let us get to know some key points about combinatorial test cases.

• Each combinatorial test case is designed to cover a specific input parameter of variable combination.
• Combinatorial test cases are created to cover a wide range of the scope since the end goal of combinatorial testing is to reduce the number of test cases.
• Combinatorial test cases are not created randomly. They are designed using specialized algorithms or tools that consider various input parameters to create test cases.
• The basic need for combinatorial test cases is to reduce the effort of testing complicated software applications focusing on critical combinations.
• Like the other types of test cases, the testers should be able to detect defects, bugs, vulnerabilities, and unexpected system behaviors when combinatorial test cases are executed.

Let’s take a combinatorial test example for a simple login scenario. Initially, a login page of a web application might contain parameters such as user name and password. Those parameters can have several inputs like this,

• Username: [User1, User2, User3]
• Password: [Password1, Password2]

If we consider this login scenario to write combinatorial test cases, we can design 6 possible combinatorial test cases for that. Those will be like the following, 

• Test Case 1: Username=User1, Password=Password1
• Test Case 2: Username=User2, Password=Password1
• Test Case 3: Username=User3, Password=Password1
• Test Case 4: Username=User1, Password=Password2
• Test Case 5: Username=User2, Password=Password2
• Test Case 6: Username=User3, Password=Password2

In this combinatorial test example, we can cover all the possible input combinations of usernames and passwords using only 6 test cases. With that, now you have an idea of how to write a minimum number of test cases to cover a broad range of the testing scope.

How to Do Combinatorial Testing?

Combinatorial testing cannot be done with the same approach that we use to perform normal component testing since it always focuses on the input parameter combinations rather than testing the initial scenario. To perform a combinatorial test, the following steps can be followed.

1. Identify input parameters and configuration options that need to be tested in the software application, including variables, settings, features, etc.
2. For each of these parameters or the configurations, define a list of possible values that represent different settings and options. (Such as different usernames, passwords, etc.)
3. Insert the list of possible values into the selected combinatorial testing tool and design the respective combinatorial test cases. Or create the combinatorial test cases manually considering the respective input combinations.
4. Execute the created test cases on your software application.
5. Analyze the results of the test execution and review the combinatorial test coverage.
6. Repeat the testing process with various input parameters and configurations if you need to.
7. Report any issues found during combinatorial test execution.
8. Continue maintenance testing by re-running combinatorial tests from time to time with necessary changes.

Manual Combinatorial Testing

When it comes to manual combinatorial testing, testers manually select and combine input parameters and their values to cover various combinations. They need to plan, design and execute combinatorial test cases while documenting the test results as well. Even though its control is with the testers, creating combinatorial test cases will be more time-consuming and it will not be much practical for the software applications with a large number of input parameters. This approach is more effective for smaller software applications with less number of input parameter combinations that the automated tools are not suitable for.

Automated Combinatorial Testing

In automated combinatorial testing, testers use specialized software tools or scripts to create and execute a large number of test cases. These automated tools use combinatorial algorithms to create test cases while considering various combinations of input parameters and configuration options. Ultimately, this approach minimizes the time and effort of manual combinatorial testing and it is more effective for software applications with a large number of input parameters.

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Why Do We Need Combinatorial Testing Tools?

Combinatorial testing tools are very important due to several reasons. Let’s take a software application that needs to be tested with a lot of input variables. Other than performing combinatorial testing manually, we can get help from the combinatorial testing tools which create a minimum number of test cases that cover a wide range of input combinations. It reduces the time and effort required for manual combinatorial testing as well. When it comes to accuracy, we can trust the test cases that were written by an automated approach rather than the manually written ones. 

Combinatorial testing tools help detect defects, vulnerabilities, and unexpected responses effectively. Most importantly, combinatorial testing tools can be effectively used when testing more complex software applications instead of doing combinatorial testing manually. Because, if testers create and execute combinatorial test cases manually for a more complex software application, there is a high chance of missing several critical test scenarios that can lead the entire software product to a high risk.

Top Combinatorial Testing Tools

Even though combinatorial testing sounds like quite a new concept, several tools can be used to perform combinatorial testing which are currently popular among quality assurance engineers. Here are some of those tools.

• ACTS (Advanced Combinatorial Testing System)
• Pict
• Hexawise

Advantages of Combinatorial Testing

Combinatorial testing has a lot of advantages that make the tester’s life easier. Let’s get to know some of those advantages.

• Combinatorial testing provides a wide test coverage with a smaller number of test cases which verifies the software application considering various input combinations.
• Combinatorial testing reduces testing effort, time, and cost, especially for software applications with a large number of input variables.
• This testing method is highly effective when it comes to detecting issues that occur due to specific input combinations.
• Combinatorial testing helps to detect issues during the earlier stages of development while reducing the cost of fixing them in later development phases.

Disadvantages of Combinatorial Testing

Even though there are plenty of advantages that the software development teams can gain from using combinatorial testing when ensuring the quality of the software applications, there is a set of disadvantages and challenges in combinatorial testing as well. Let’s get to know some of those disadvantages and challenges.

• Combinatorial testing may become more complex when dealing with a huge number of input parameters and values. It will be a bit challenging for the testers to manage those combinations manually.
• Since the testers may need to use specialized tools to perform automated combinatorial testing, it will take considerable time and effort for the testers to dive into those new tools.
• Automated combinatorial testing tools may require more computing resources and it will be challenging for the software projects which function under less number of resources.
• Combinatorial testing focuses on specific input combinations and sometimes they may not represent real-world user behavior.
• With the changes that are getting added to the particular software application, combinatorial test cases should be updated and well-maintained from time to time.

Conclusion

Combinatorial testing helps the testers to effectively verify the behaviors of a software application by designing and executing test cases considering various combinations of input variables and configurations. This testing approach is very beneficial especially when it comes to software applications with a huge complexity. Ultimately, combinatorial testing covers a wide scope of testing with less number of test cases while reducing the cost, time, and effort. Even though there are a few disadvantages, with the usage of the most suitable tools and adhering to the correct combinatorial test design steps, the testers can tackle those challenges and get the maximum out of combinatorial testing. All in all, combinatorial testing is the best way of giving the maximum test coverage with the minimum number of test cases.

Frequently Asked Questions

What is Combinatorial Testing in Game Testing?

Testers use combinatorial testing to test games to verify their behavior against various combinations of input parameters and gaming scenarios. This approach helps game testers and developers identify defects, gameplay issues, and unexpected interactions under specific combinations of playing actions, player characters, and certain conditions. Performing combinatorial testing in the gaming industry is very important since we all know that there can be millions of game-playing combinations available due to the number of players that use the particular games and the differences in the behavior of each game player.

What is Combinatorial Design in Software Testing?

Combinatorial test design allows the testers to create a well-structured and efficient set of test cases to validate a particular software application. While doing combinatorial design, the testers may have to select various combinations of input parameters and configurations to make sure that those test cases deliver the maximum test coverage. An effectively designed combinatorial test set helps identify defects, bugs, vulnerabilities, and unexpected application behaviors while reducing the cost, effort, and time of testing.