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Test Case Design Technique: Pairwise Testing

Overview​

Pairwise Testing (also known as All-Pairs Testing) is a black-box test design technique used to reduce the number of test cases needed when testing combinations of multiple input parameters.

Rather than testing every possible combination, pairwise testing ensures that all possible pairs of input values are covered at least once. Research has shown that most defects are caused by interactions between two parameters, making this approach highly efficient.

Why Use Pairwise Testing?​

  • Reduces the explosion of combinations in multi-variable systems
  • Offers high coverage with fewer test cases
  • More efficient than exhaustive testing
  • Ideal for configuration testing, form validations, API parameters, and device compatibility matrices

Basic Concept​

Let’s say a system has 3 input fields:

  • Browser: Chrome, Firefox
  • OS: Windows, macOS
  • Language: English, Spanish

Total combinations = 2 × 2 × 2 = 8 (full factorial testing)

Using pairwise testing, we can reduce this to 4 test cases while still covering all pairs of values at least once.

Example​

Input Parameters​

ParameterValues
BrowserChrome, Firefox
OSWindows, macOS
LanguageEnglish, Spanish

Pairwise Test Cases (Generated via Tool)​

Test CaseBrowserOSLanguage
TC01ChromeWindowsEnglish
TC02FirefoxWindowsSpanish
TC03ChromemacOSSpanish
TC04FirefoxmacOSEnglish

✅ Every possible pair (e.g., Firefox + Windows, Firefox + macOS, Chrome + English, etc.) appears at least once.

Tools to Generate Pairwise Tests​

Since manually deriving pairwise combinations can get complex with more parameters, there are several tools to automate it:

  • PICT (Microsoft tool)
  • AllPairs (from Perl)
  • Pairwise Online Tools (e.g., pairwise.teremokgames.com)
  • Hexawise
  • TestersDesk Pairwise Generator

Real-World Use Cases​

  • Mobile App Testing across devices, OS, screen sizes
  • Web App Testing with combinations of browsers, languages, login types
  • Payment Gateway Testing with card types, currencies, transaction types
  • API Testing with different request parameters and headers

Limitations​

  • Doesn’t cover three-way or higher interactions (but extensions like orthogonal arrays can help)
  • Not suitable for scenarios where specific sequences or state dependencies are critical
  • Best when parameters are independent of one another

Best Practices​

  • Use pairwise for combinatorial explosion problems (3+ variables)
  • Confirm parameter independence before using
  • Combine with equivalence partitioning or boundary value analysis for thorough coverage
  • Document the rationale and tools used for transparency

Summary​

Pairwise Testing is a smart, efficient way to test multi-variable systems without being overwhelmed by combinations. It gives strong coverage where it matters most—interactions between pairs of inputs.

“Test smarter, not harder. Pairwise testing gives you 80% of the value with 20% of the effort.”

Quick Template​

Parameter 1Parameter 2Parameter 3
Value AValue XValue 1
Value AValue YValue 2
Value BValue XValue 2
Value BValue YValue 1

Every pair of values from each column will appear at least once.