What's the difference between load vs stress testing?

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Posted by Brian Borg

Load testing and stress testing are both types of performance tests. However, they have different purposes and approaches. It's vital to understand these differences. That way, you test more effectively and avoid the pitfall of substituting one test for the other.

What is load testing?

Load testing is where you put demand on a software system and measure the response. This can apply to modeling multiple users at various stages of use in the application, or even by running large processing tasks. Generally, load testing will offer insight into slow performance under anticipated normal loads and can be used to identify bottlenecks.

What is stress testing?

Stress testing allows you to put a system under heavy lead, beyond what is considered 'normal' usage patterns, to assess breaking points. It is often applied to specific parts of an application, such as the checkout process on an e-commerce site, to evaluate the capacity and robustness of these higher-priority parts of the user journey.

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What are the key differences?

Both testing types give the tester an idea of the maximum performance of the application under various circumstances. They can both uncover issues that affect performance over time, such as memory leaks. But, these testing types are different. Here's how:


Load testing is run on the whole environment and database, looking at things like latency, server or processing issues that lead to poor response times. This type of testing is designed to put a system under a heavy load and see how it responds overall.

Stress tests are usually applied in a more targeted way. Stress testing takes into account user concurrency, denial of service attacks and resourcing around key touchpoints. These tests measure the response of individual transactions to see if they recover, how quickly, and to what extent.


The desired outcome of load testing is a positive result, with the system able to manage expected traffic or processing requirements.

With stress testing, the outcome is almost always going to be failure, but the purpose is to raise the bar on when that failure occurs. Ideally, it would fail at such high levels of traffic, or other system stressors, that outside of staging, the application will not fail.

So, should you do both load and stress testing?

The answer, as usual, is to do both. Each type of testing gives you valuable information about your software system. But, if you're absolutely pressed for time or resources, then we recommend choosing stress testing as, from this, you learn more about critical fail points than load testing.

However, for your next project, listen to this wise comment from Bill Gates: 'We have as many testers as we have developers. And testers spend all their time testing, and developers spend half their time testing.' And, according to Global Market Insights, the industry share of software testing is expected to grow by more than 6 percent from 2020 to 2026.

Clearly, testing is the priority in software development. It's up to you to put it at the top of your to-do list. Implement a 'shift left' model, bringing your testers into the strategy phase of your development, and test more widely, and more often. Spread the load. Avoid the stress.

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