What is Pairwise Testing in Software Development?
For those looking to maximize testing resource efficiency, pairwise testing can be a useful tool to produce higher-quality software within time or budget constraints. Below, we explore what pairwise testing is, provide concrete examples, reasons to incorporate it, why some may not find it valuable, and how to implement this type of testing (should you decide to use it).
What is Pairwise Testing?
Also known as “all-pairs testing,” this method assesses every possible combination of input parameter pairs to identify defects or issues. The name comes from its focus on pairs of input variables rather than testing all possible multi-factor combinations (which may not be feasible for larger, more complex systems). This not only verifies that no couplings create bugs, but also tests how the different inputs and parameters interact with each other.
For example (we’ll discuss more specific ones below), let’s say your system has three settings — A, B, and C, each with multiple possible inputs. Pairwise testing would check that every combination of values between each pair (A + B, A + C, and B + C) is covered at least once in test cases.
What is the Goal?
While it sounds exhausting, this should ideally lead to fewer test cases created during the testing process. This is because it prevents the exponential increase in test cases that would otherwise result from expanding testing scope beyond simple pairs of values (e.g. to interactions between three or more factors). To put this in perspective, if your software has:
- 4 input variables
- 5 possible values for each
Total coverage of every possible combination would result in 625 different test cases (54). On the other hand, pairwise testing would only require about 20 test cases to cover the various couplings.
Three Real-World Examples of Pairwise Testing
Let’s take a closer look at some more specific examples in the context of real software development projects.
Example 1: Web-Based Survey Form
A multi-step survey form for correct data handling and navigation.
Variables:
- User Role: Admin, Registered User, Guest
- Device: Desktop, Mobile, Tablet
- Browser: Chrome, Firefox, Safari, Edge
- Survey Completion Path: All Questions, Skipped Optional Questions
Exhaustive testing would require 3 × 3 × 4 × 2 = 72 different test cases. Using pairwise testing, the number could be reduced to around 10 to 15, covering every possible pair like Admin + Desktop, Mobile + Safari, etc. but skipping unnecessary combinations with more than two variables.
Example 2: E-Commerce Checkout System
The checkout process for an online shopping platform.
Variables:
- Payment Method: Credit Card, PayPal, Gift Card
- Shipping Method: Standard, Expedited, Same-Day
- Device: Desktop, Mobile, Tablet
- Promo Code: Valid, Invalid, None
With four variables and several values each, exhaustive testing would require 3 × 3 × 3 × 3 = 81 test cases. Pairwise testing can reduce this dramatically, saving time and still ensuring that all combinations of input pairs (like payment method + device) are tested.
Example 3: Airline Booking System
A flight booking interface with multiple input parameters.
Variables:
- Ticket Type: Economy, Business, First Class
- Payment Method: Credit Card, Debit Card, PayPal
- Traveler: Adult, Child, Senior, Infant
- Destination: Domestic, International
- Seat Preference: Window, Aisle, No Preference
Testing every possible configuration requires 3 × 3 × 4 × 2 × 3 = 216 test cases. Pairwise testing would reduce the required number to about 20 to 30, testing critical combinations like Business Class + Credit Card, Senior Traveler + Window Seat, etc.
Benefits
As we’ve discussed, there are a host of advantages that come with pairwise testing, particularly when it comes to time-saving in systems with lots of factors and inputs. However, there are other reasons to consider this testing method as well:
- Reduces Redundancy: Increased test coverage typically results in higher rates of test redundancy as well, which pairwise testing limits due to its coupled approach and eliminating duplicate combinations.
- High Defect Detection: This increased coverage and efficiency leads to better defect detection without expending resources that would have diminishing returns and less likelihood of producing bugs.
- Ideal for Limited Budget: The time saved on avoiding redundant testing and making the most of constrained resources is a major advantage for testing teams with limited budget who still need to ensure excellent quality.
- Easy Tool Implementation: There are several easy tools (like PICT and Pairwise Online Generator) that automatically create test case sets, making it easy for teams to generate without complex mathematical knowledge of combinatorial techniques
- Versatile Across Platforms: Because pairwise testing can be applied to any scenario involving multiple inputs with different values, it can be used across web platforms, mobile apps, different hardware, etc.
Disadvantages & Challenges
On the other hand, there are some factors that make it less ideal and it has limitations that may not cut it for certain scenarios:
- Limited to Pairs: As we’ve explored, this type of testing only evaluates two inputs at a time, which may miss defects caused by interactions of three or more inputs (e.g. a bug that only appears for a combination of “Payment Method + Device + Browser”).
- Not Suitable for More Complex Systems: Because of this limitation to only two inputs at a time, pairwise testing isn’t ideal for systems where issues are known to come from multi-factor interactions that would require more comprehensive testing.
- Complicated Test Case Creation: Although the tools mentioned above can simplify test case generation, it still requires careful planning and attention to detail so variable dependencies are accounted for and all major combinations are covered.
- Dependent on Input Selection Quality: On that note, the selection of inputs (which makes up the pairs) will make or break pairwise testing’s effectiveness — if low-relevance variables are included or important values are left out, time may be wasted and critical bugs may be missed.
- May Require Further Testing: Pairwise testing’s benefits largely come from how it makes coverage sacrifices to increase efficiency. Because of this, additional testing methods might be needed to polish the final application.
When Should You Use Pairwise Testing?
So who should consider incorporating pairwise testing, and under what circumstances? The best candidates for this type of testing are teams with limited resources, projects that have independent inputs (that have a low chance of multi-factor interaction bugs), and Agile development teams. The last one may seem less obvious, but Agile teams are always looking to improve workflow efficiencies, and the iterative nature of these frameworks benefits from faster testing (which pairwise provides).
Common scenarios when pairwise testing would be recommended include early integration testing, configuration testing, regression testing, and when defect patterns or histories are not well-known. These all gain value from rapid pairwise testing to lay the groundwork. However, pairwise testing would not be comprehensive enough for evaluations like security testing in regulated industries.
Best Practices for Effective Testing
If you decide to adopt pairwise testing based on the above criteria and recommendations, here are some tips to maximize its effectiveness and value for your team:
- Choose the Proper Inputs: As mentioned above, the crux of pairwise testing is the variable and value selection, so carefully consider and plan what should be included for optimal test coverage and relevance.
- Prioritize Higher-Risk Pairs: Because of its somewhat limited scope, concentrate testing around the more critical interactions, such as dependencies or frequently-used combinations.
- Use Quality Testing Tools: Your testing is only as insightful and valuable as the tool you use, so find a platform that has all the necessary functionality, preferably with additional testing options to support your entire pipeline.
- Supplement With Other Testing: Speaking of the entire pipeline, pairwise testing is probably not the only method you’ll use, so be sure to leverage other techniques for a more comprehensive assessment of your product throughout the lifecycle.
- Validate Assumptions Before Execution: Ensure that variables are independent of each other unless clearly stated otherwise — this will save you time and headaches from having to untangle data, making the process more efficient and realistic.
- Meticulously Analyze Results: If a test case fails, thoroughly review and assess whether the cause was a genuine defect or a flaw in the test case design (and document combinations that caused failures for future testing).
- Continuously Refine Coverage: As features are added or configurations are adjusted, inputs and values will need to be kept up-to-date, refining the variable selection and risk prioritization as you develop.
Pairwise Software Testing FAQs
How effective is it at finding bugs?
Pairwise testing is very efficient at finding bugs because of its focus on variable combinations that cause the most defects (two-factor interactions). This is further enhanced when used continuously, such as in Agile development cycles.
Can it be automated?
It can (and should) be streamlined with capable automated testing tools to simplify the combinatorial mathematics and test case creation. However, this still relies heavily on careful planning and input selection prior to execution.
How can you generate pairwise test cases?
Start by identifying relevant input parameters and the values that each can represent. If done with an automated tool, feed this data into the system to create a matrix of unique pairs, which should then generate test cases based on each. If done manually, work through each parameter, matching individual values to other parameter values until all possible combination pairs are assigned. Then, design test cases that capture the various combinations of inputs, and validate each before moving on to the test execution step.
Looking for a Better Testing Tool?
Many of the pairwise testing tools out there can simplify the test case generation process within this specific framework, but what if you want to perform other types of testing? SpiraTest is the ideal solution, as it offers pairwise testing automation, but also includes a powerful toolkit of other features and integrations to serve as your central testing hub. From requirements management and time-saving automated testing to customized reporting dashboards, it’s the most capable software testing tool on the market. Hear from our partners about what makes SpiraTest so great, or try a free 30-day trial to see for yourself!