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17 October, 2023

The Pareto Principle: 6 Ways to Test Smarter With The 80-20 Rule

the pareto principle

In many ways, software testing is the art of doing more with less. Efficiency is the name of the game. Testing teams are constantly pressured to mitigate critical business risks without delaying go-live and are often encouraged to abandon best practices when timings get tight. However, by adopting the Pareto principle, I will show you 6 ways you can get ahead of the game and test smarter and faster.

Testing is a potentially open-ended endeavour with many combinations and permutations.

Knowing how and where to focus your effort is a massive part of effective test management. To be a great test manager, you need an easy rule of thumb that lets you quickly assess the testing priorities for your current project.

Throughout my 3 decades in software development, nothing has been more effective than the Pareto Principle, also known as the 80-20 rule.

The 80-20 rule applies to many areas of software testing. Once you understand how to use it to your advantage, testing becomes so much easier.

What is The Pareto Principle?

Initially observed by Vilfredo Pareto, an Italian economist, he noticed that roughly 80% of the land in Italy was owned by 20% of the population. This observation soon proved relevant across different domains.

Microsoft further demonstrated that fixing the top 20% of the most reported bugs would eliminate 80% of the related errors and crashes in a given system.

Why The Pareto Principle is Important for Software Testing?

The 80-20 rule can be applied to many software testing situations, making it an essential concept for testers and quality assurance professionals to understand.

Of course, in an ideal world, we testers typically want to cover more than our time or resources will allow. However, this isn’t possible, especially in today’s high-paced projects. Instead, we must be pragmatic and test what matters most in the available time.

You can spend a lot of time developing intricate risk-based testing plans or use the Pareto principle as an effective rule of thumb and get started quickly.

Six Ways the Pareto Principle Helps You Test Smarter and Faster:

  1. Efficiency and Focus: Roughly 20% of the software components are often responsible for around 80% of defects and issues. Knowing this, testers can allocate resources more efficiently and focus on the most critical parts of the software.

Consider an e-commerce application where most defects have been found in the checkout and payment modules. Following the Pareto Principle, testers would focus 80% of their early testing effort on thoroughly testing these modules, expecting they might continue to be defect-prone.

  1. Risk-based Testing: 20% of an application’s processes will potentially carry 80% of the business risk. The Pareto Principle suggests that testers can uncover most defects by concentrating their integration testing on these high-risk processes.

For example, fund transfers and account balance processes might be deemed high-risk in a banking application due to financial implications. Testers would prioritise these areas as defects would have more severe consequences than defects in less critical modules.

  1. Device Testing: Testing teams are often under-resourced, having to do more with less. Add virtually unlimited mobile devices to that mix, and you have a problem. By applying the Pareto Principle, teams can optimise the allocation of resources (time, personnel, infrastructure) to yield the highest defect detection.

Instead of testing an ever-growing number of devices, test teams should focus 80% of their mobile testing effort on the most critical 20% of devices, ensuring they catch the most important issues.

  1. Prioritising Bug Fixes: Once defects are identified, a few major underlying bugs will likely cause issues across multiple requirements or have a higher risk impact. Development teams can use the Pareto Principle to prioritise bug fixes. As Microsoft found, addressing the top 20% of the bugs that cause 80% of the high criticality issues can significantly improve the software’s reliability and user experience.

Let’s say that after testing, 100 defects are found. 20 defects are causing issues in multiple processes, whereas 80 defects affect just a single process. Developers would prioritise fixing these 20 defects before addressing the remaining 80, which might be minor UI glitches or rare edge cases.

  1. Test Case Optimisation: Over time, as more and more test cases get added, it’s essential to identify which test cases yield the most value. The Pareto Principle can guide testers in focusing on and maintaining the most valuable test cases while reconsidering or deprioritising others.

Over time, an application can accumulate thousands of test cases. Analysis shows that 20% of these test cases find 80% of defects. Testers can focus on maintaining and running these critical test cases regularly, while the less impactful ones might be run less frequently or be candidates for removal.

  1. Cost Savings: By focusing on the most impactful areas, teams can reduce testing and defect mitigation costs. The cost of fixing a defect increases exponentially the later it is found, so finding and addressing critical defects early can result in substantial cost savings.

Imagine that an enterprise software application is in its final phase before release. You could test every feature thoroughly and quickly rack up weeks or months of testing. Alternatively, you focus 80% of your time on the top 20% of features that historically caused most post-release customer complaints. Leaving 20% of your time to lightly test the remaining areas.

Final Thoughts

The Pareto Principle provides a quick and effective rule of thumb to ensure that you focus your resources on what will have the most impact and benefit.

It isn’t about cutting corners or reducing the importance of comprehensive testing. It’s about concentrating on key areas and deploying effective and efficient effort where it is needed.

Understanding and applying the 80-20 rule will help your projects produce better products and let you maximise your available resources.

With today’s rapid development cycles, the need to test smarter, better, and faster has never been more critical. By leveraging the insights of the Pareto Principle, testing teams can rise to the occasion, ensuring high-quality software and rapid development.

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Stephen Davis
by Stephen Davis

Stephen Davis is the founder of Calleo Software, a OpenText (formerly Micro Focus) Gold Partner. His passion is to help test professionals improve the efficiency and effectiveness of software testing.

To view Stephen's LinkedIn profile and connect 

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