user acceptance testing

What is Orthogonal Array Testing? | Why & How to Perform?

Orthogonal Array Testing is a statistical method designed to help testers examine multiple variables, their interactions, and their possible combinations, all while minimizing the number of test cases. In essence, OAT focuses on achieving maximum test coverage with the minimum number of tests, making it a highly efficient testing method.

The key to understanding the power of orthogonal array testing lies in its ability to identify defects efficiently, providing a high return on investment in terms of time and resources. OAT has emerged as a powerful and efficient method to streamline the testing process, making it a vital tool for developers and testers alike. This article will delve into what orthogonal array testing is and why it’s such a valuable technique in software quality assurance.

What is Orthogonal Array Testing?

Orthogonal Array Testing is a systematic and statistically driven software testing technique. Its primary objective is to uncover defects and issues within software applications efficiently and comprehensively while minimizing the number of test cases required. This method is particularly valuable in situations where exhaustive testing of all possible combinations and permutations is impractical or time-consuming, as it helps strike a balance between test coverage and resource efficiency.

At its core, OAT relies on the principle of orthogonal arrays, which are mathematical constructs used to represent combinations of variables in a way that ensures critical interactions are tested. These arrays are based on combinatorial mathematics, allowing testers to explore various scenarios while covering a significant portion of the input space with fewer test cases.

The idea behind orthogonal array testing is to identify and prioritize the most critical scenarios and combinations that are likely to reveal defects, reducing the overall testing effort and the time required to validate the software. This makes OAT particularly useful in industries where rigorous testing is essential, such as software development, hardware testing, and manufacturing.

Why Use Orthogonal Array Testing?

Orthogonal Array Testing (OAT) is a valuable testing technique due to its inherent efficiency and effectiveness. By systematically selecting a subset of test cases that cover a wide range of variable combinations, OAT achieves comprehensive test coverage while conserving time and resources. This not only accelerates the identification of defects but also reduces the overall testing effort, making it a preferred choice for teams aiming to enhance their software quality without compromising on productivity.

In real-world projects, resources are often limited, and prioritization is essential. Orthogonal array testing helps teams allocate their resources more efficiently by targeting high-impact test scenarios and variable combinations. Moreover, it allows you to enhance test maintenance. As software evolves, so do the testing requirements. OAT’s ability to provide maximum test coverage with fewer test cases simplifies the task of maintaining test suites. Testers can adapt to changes more efficiently, reducing maintenance overhead.

Orthogonal Array Testing Characteristics

A few unique characteristics of Orthogonal Array Testing are – 

  • Efficiency: One of the primary characteristics of orthogonal array testing is its ability to achieve efficient test coverage. It reduces the number of test cases required, making it a cost-effective and time-saving approach compared to exhaustive testing methods.
  • Combinatorial Approach: OAT is rooted in combinatorial mathematics, allowing it to systematically select test scenarios and variable combinations. This ensures that critical interactions are tested while minimizing redundant tests.
  • Early Defect Detection: OAT is instrumental in early defect identification. By prioritizing the most critical test scenarios, it helps detect and rectify defects at an early stage of development, reducing the risk of costly post-release fixes.
  • Resource Optimization: The technique enables optimal resource allocation by focusing on high-impact test scenarios and variables. This makes it a strategic choice for situations where resources are limited or need to be used efficiently.
  • Applicability: Orthogonal array testing is not limited to software testing alone; it can be applied in diverse fields such as hardware testing, manufacturing, and experimental design, where the efficient use of resources and comprehensive testing are paramount.

How to Utilize Orthogonal Array Testing Technique?

To harness the power of Orthogonal Array Testing (OAT) effectively, it’s essential to follow a structured approach. Start by identifying the variables and factors relevant to your software or product. Next, create an orthogonal array that represents the possible combinations of these variables. Carefully select a subset of test cases from the array, ensuring it covers a wide range of scenarios. Execute these test cases, observing the behavior of your system under varying conditions.

It’s crucial to document and analyze the results meticulously, as this will reveal defects, conflicts, and issues. As you iterate and refine your test cases, you’ll be able to improve the quality of your software while conserving resources. OAT’s efficiency and systematic approach make it a valuable addition to your testing toolbox, enhancing the overall reliability and robustness of your products.

Examples of Orthogonal Array Testing

Orthogonal Array Testing (OAT) can be better understood through practical examples. Here, we will explore two scenarios where OAT proves its effectiveness in software testing and beyond.

Example 1: Testing a User Registration Form

Imagine you are testing a user registration form for a web application. The form includes various fields like name, email, password, and date of birth, each with multiple potential input values. OAT can simplify the testing process by using an orthogonal array to select a representative subset of test cases, covering various combinations of inputs. For instance, you can create an orthogonal array that ensures all possible combinations of valid and invalid inputs are tested, including different lengths of passwords, valid and invalid email formats, and various date of birth formats. 

Suppose we want to test a user registration form with three variables: password length (Short, Medium, Long), email format (Valid, Invalid), and date of birth format (Valid, Invalid). To efficiently cover the possible combinations, we can use the following orthogonal array.

Test CasePassword LengthEmail FormatDate of Birth Format
Test Case 1ShortValidValid
Test Case 2ShortInvalidInvalid
Test Case 3ShortValidInvalid
Test Case 4ShortInvalidValid
Test Case 5MediumValidValid
Test Case 6MediumInvalidInvalid
Test Case 7MediumValidInvalid
Test Case 8MediumInvalidValid
Test Case 9LongValidValid
Test Case 10LongInvalidInvalid
Test Case 11LongValidInvalid
Test Case 12LongInvalidValid

This orthogonal array allows us to cover all possible combinations of the three variables efficiently with only twelve test cases.

Example 2: Manufacturing Quality Control

Orthogonal Array Testing is not limited to software; it’s applicable in manufacturing processes as well. Let’s consider a scenario in which a company manufactures electronic circuit boards. In this case, OAT can help optimize the testing of various components on the boards, such as resistors, capacitors, and connectors. By using an orthogonal array, you can select specific combinations of components to test. For example, if you have different resistance values, capacitor sizes, and connector types, OAT enables you to test a subset of these components efficiently, covering various combinations.

Let’s consider three variables: resistor value (R1, R2, R3), capacitor size (C1, C2, C3), and connector type (T1, T2, T3). We can use an L27 orthogonal array, which is a suitable choice for testing three variables with three levels each.

How to do Orthogonal Array Testing?

Here’s a step-by-step process on how to perform Orthogonal Array Testing.

  1. Identify Variables and Levels: Begin by identifying the variables in your testing scenario. Variables represent the different factors or attributes you want to test. For each variable, determine its levels, which are the specific values or states that it can take. For example, in testing a login form, variables might include username, password, and authentication method, each with multiple levels.
  1. Create an Orthogonal Array: Select an appropriate orthogonal array that matches the number of variables and their levels. The specific orthogonal array you choose depends on the project’s requirements.
  1. Generate Test Cases: Utilize the selected orthogonal array to generate a set of test cases. Each row in the orthogonal array represents a unique combination of variable levels, forming a test case. For instance, if your orthogonal array has three rows, you’ll have three test cases, each covering a different combination of variables and levels.

    You can use automated testing tools like Testsigma to create, manage, execute, and monitor your test cases. Testsigma is an AI-powered automated testing tool with more than 3000+ combinations of devices, browsers, and OS. With Testsigma, you can easily create test cases in simple natural English language.

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For example, suppose you want to create an automated test case for web testing of a login page. Here are the steps you can create in testsigma in minutes.

  1. Navigate to Simply Travel login page(
  2. Enter username as ‘admin’ in the User Name field.
  3. Enter the password as ‘12345’ in the Password field.
  4. Click on the login button.

You can also easily enter your test data in the test steps.

Testsigma Step Recorder chrome extension also lets you generate automated test scripts from a series of manual actions you take to play out a test scenario. The automated test scripts can then be run on all the available Web Browsers.


  1. Test Execution: Execute the generated test cases in your testing environment. This step involves performing the actual tests based on the combinations of variable levels as defined in the orthogonal array. While executing test cases, tools like Testsigma can help automate the process, saving time and ensuring consistency.


  1. Analysis and Defect Detection: Analyze the test results to identify defects, inconsistencies, or issues in the software. Look for unexpected behavior or discrepancies in the outcomes. Logging and tracking defects is essential for subsequent resolution and verification.

    With Testsigma, you can easily debug and monitor your test case executions.

  2. Refinement and Iteration: Based on the analysis, you may need to refine the orthogonal array, add new variables, or adjust the levels to improve test coverage. The iterative nature of OAT allows you to fine-tune the testing strategy to enhance its effectiveness.

Try out Testsigma for free and automate your complete testing suite!

Advantages of Orthogonal Testing

Orthogonal Array Testing (OAT) offers several advantages that make it a valuable approach in software and quality assurance:

  • Combinatorial Coverage: OAT systematically explores the entire input space by selecting test cases that represent combinations of variables and their interactions. This comprehensive coverage ensures that no critical scenario is overlooked.
  • Statistical Rigor: OAT is rooted in combinatorial mathematics and statistical principles. This technical foundation ensures that the selected test cases are representative of real-world usage, improving the reliability of testing results.
  • Reduced Test Case Count: OAT’s technical design minimizes the number of test cases required to achieve a high level of coverage. This reduction leads to significant time and resource savings during test execution.
  • Quantifiable Results: OAT provides quantifiable metrics for test coverage, helping testers and developers gauge the completeness of their testing efforts. This technical data is valuable for assessing the quality of the product and identifying areas that require further testing.
  • Tool Integration: Several specialized tools and software packages are available for generating orthogonal arrays and analyzing test results. This technical advantage streamlines the implementation of OAT and makes it accessible to a broader range of technical teams.

Disadvantages of Orthogonal Array Testing

While Orthogonal Array Testing (OAT) offers numerous advantages, it also has some limitations:

  • Complex Selection: Creating an appropriate orthogonal array can be complex and requires a good understanding of combinatorial mathematics. This complexity may deter some teams from adopting OAT.
  • Limited to Quantifiable Variables: OAT is most effective when dealing with quantifiable variables. It may not be suitable for testing qualitative or non-numeric aspects of a system, such as user experience or subjective features.
  • Initial Setup Overhead: Setting up OAT for a project may require an initial investment of time and effort. This can be seen as a disadvantage when compared to quick and straightforward testing methods.
  • Risk of Missing Interactions: While OAT aims to cover critical interactions efficiently, there’s still a risk that some interactions may be missed. If a particular interaction is not considered during the design of the orthogonal array, it won’t be tested.
  • Applicability Challenges: OAT may not be suitable for all types of software or industries. Some projects or systems may not benefit from the efficiency of OAT, and its applicability can vary depending on the context and testing requirements.

Mistakes or Errors While Performing OAT

Here is a list of a few errors or mistakes that you might perform while working with orthogonal array testing methodology.

  • Incomplete Variable Consideration: One common mistake is failing to consider all relevant variables or factors in the testing process. If key variables are omitted when creating the orthogonal array, critical interactions may be overlooked, potentially leading to untested scenarios.
  • Incorrect Orthogonal Array Selection: Choosing an inappropriate orthogonal array for the specific testing scenario can be an error. The selected array should match the number of variables and their levels, and it should reflect the complexity of the system accurately.
  • Neglecting Real-World Scenarios: OAT, while efficient, may not always account for real-world usage scenarios. Testers might overlook some unique or rare situations that could be important in practice. It’s essential to balance efficiency with the need for practical coverage.
  • Misinterpretation of Results: Misinterpreting the results of OAT can also be a potential error. Testers may misjudge the significance of detected defects or overestimate the coverage achieved. Accurate analysis and understanding of the results are crucial to making informed decisions about software quality.

How to Measure the Effectiveness of OAT?

Measuring the effectiveness of Orthogonal Array Testing (OAT) is critical to ensure that it contributes positively to the quality assurance process. One key metric to consider is the test coverage achieved by OAT in relation to the total possible combinations. This can be quantified by comparing the number of test cases executed using OAT to the exhaustive number of test cases that would be required for full coverage. A higher ratio of coverage achieved with fewer test cases signifies the efficiency and effectiveness of OAT. 

Additionally, analyzing the defects detected during OAT can provide insights into the technique’s effectiveness. If OAT helps uncover a significant portion of critical defects early in the testing process, it demonstrates its value in improving software quality and saving resources.

How to Choose an OAT Tool?

Selecting the right Orthogonal Array Testing (OAT) tool is essential for successfully implementing this technique. Here are steps to guide you in choosing an OAT tool:

  • Assess Testing Needs: Begin by understanding your testing requirements, such as the number of variables, their levels, and the complexity of interactions. A clear grasp of your project’s scope will help you identify the most suitable tool.
  • Consider Integration: Ensure that the OAT tool integrates seamlessly with your existing testing environment, including other testing tools and frameworks. Compatibility and interoperability are crucial for a smooth workflow.
  • Evaluate Feature Set: Examine the features offered by each tool. Consider factors such as the tool’s ability to generate orthogonal arrays, analyze results, and visualize test coverage. Robust reporting and visualization features can enhance the effectiveness of OAT.
  • User-Friendly Interface: A user-friendly interface and intuitive navigation are valuable, as they facilitate efficient use of the tool. It should allow test designers and analysts to work comfortably and effectively.
  • Customization Options: Look for a tool that offers customization options. The ability to tailor the tool to your specific project requirements is essential for flexibility and adaptability.
  • Vendor Support and Training: Assess the level of vendor support and training available. Adequate support can be vital for resolving issues and gaining expertise in using the tool effectively.
  • Cost and Licensing: Consider your budget and licensing requirements. Compare the costs of different tools and evaluate their pricing models. Choose a tool that fits within your budget and aligns with your organization’s licensing needs.
  • Trial and Evaluation: Whenever possible, take advantage of trial versions or evaluations offered by the tool vendors. Test the tool with a small project or a subset of your testing requirements to assess its suitability.
  • Scalability: Ensure that the chosen tool can scale to meet the demands of your projects, both in terms of the number of test cases and the complexity of variable interactions.

By following these steps, you can systematically evaluate and choose the OAT tool that best aligns with your testing needs and ensures the successful implementation of orthogonal array testing in your quality assurance processes.

How to use an OAT Tool Effectively?

Effectively utilizing an Orthogonal Array Testing (OAT) tool involves a systematic approach. Start by thoroughly understanding the tool’s features and capabilities. Define your testing objectives, including the variables and their levels, and create a clear test plan. Collaborate closely with the tool’s users, such as testers and analysts, to ensure they receive proper training and guidance on tool utilization. Regularly review and refine your OAT strategy to adapt to evolving project requirements. By continually monitoring and optimizing the tool’s usage and aligning it with your testing goals, you can harness the full potential of OAT for efficient and comprehensive testing.

What are Some Challenges and Limitations of OAT?

Here are a few challenges and limitations of adopting OAT in your testing pipeline.

  • Complexity in Orthogonal Array Design: Creating an appropriate orthogonal array can be challenging, particularly for projects with numerous variables and complex interactions, requiring a good understanding of combinatorial mathematics.
  • Incompatibility with Qualitative Testing: OAT is most effective with quantifiable variables and may not be suitable for testing qualitative or non-numeric aspects of a system, such as user experience or subjective features.
  • Risk of Missing Critical Interactions: Despite its efficiency, there is a risk of missing some critical interactions if not all relevant variables are considered during orthogonal array design.
  • Tool Dependency: OAT often relies on specialized tools, and not all projects or organizations may have access to or be able to afford these tools, limiting its adoption.
  • Initial Setup Overhead: Setting up OAT for a project may require an initial investment of time and effort in designing the orthogonal array, which can be perceived as a limitation compared to more straightforward testing methods.
  • Resource Constraints: OAT may require skilled personnel who understand the mathematical concepts behind orthogonal arrays, which may pose a challenge for organizations lacking in-house expertise.
  • Limited Real-World Context: OAT may not account for all real-world usage scenarios, potentially neglecting rare or unique situations that could be essential in practice.
  • Continuous Maintenance: As the system evolves, the orthogonal array may require updates, which can add complexity and maintenance overhead, especially in long-term projects.


In conclusion, Orthogonal Array Testing (OAT) stands out as a powerful and efficient technique in the realm of software testing and beyond. Its ability to optimize test case selection while maintaining comprehensive coverage makes it a valuable addition to any quality assurance toolkit. OAT’s advantages in terms of efficiency, early defect detection, and resource optimization provide clear benefits in cost reduction and enhanced product quality. 

However, it’s crucial to acknowledge the challenges and limitations it presents, such as the initial setup overhead and the potential for missing certain interactions. Nevertheless, when applied judiciously, OAT can significantly improve testing processes and contribute to the development of reliable, high-quality software.

Frequently Asked Questions

Is Orthogonal array useful for reducing test cases?

Absolutely, orthogonal arrays are highly useful for reducing the number of test cases required in a testing process. By systematically selecting a representative subset of test scenarios that cover various combinations of variables, orthogonal array testing achieves extensive test coverage with a minimal number of test cases. This not only saves time and resources but also ensures that critical interactions are tested. OAT’s efficiency in reducing test case count while maintaining comprehensive coverage makes it a valuable strategy for efficient and effective testing.

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