The Role of Sanity Testing in Performance Engineering

As a CTO, my role extends beyond overseeing technical solutions — I work closely with engineering teams to ensure performance testing strategies align with business goals. One of the recurring challenges I’ve observed is how sanity testing, despite being a simple step, often determines the success or failure of performance testing efforts. 

Many teams focus on running large-scale performance tests, ensuring their applications can handle peak loads, but neglect the essential first step — validating the test scripts and basic system functionality before executing a full-scale load test. Over the years, I’ve seen how overlooking this step can lead to wasted time, misleading results, and frustration.

Conversations With Clients: Lessons Learned

Over time, I’ve had numerous discussions with teams struggling with performance testing failures. One common theme? Tests failing not because the system couldn’t handle the load, but because of incorrect test configurations, missing parameters, or broken scripts.

One memorable conversation was with a lead engineer at a financial services company. They had spent weeks designing an elaborate test to simulate thousands of concurrent users. When the test launched, response times were erratic, and transactions were failing randomly. After hours of debugging, we discovered that the test scripts weren’t handling session persistence correctly. A quick sanity test beforehand — executing a small-scale test with just a few virtual users — would have flagged this issue within minutes. Instead, the team lost two days troubleshooting.

Another case involved a retail company preparing for a Black Friday event. Their load test reported intermittent checkout failures. The team initially assumed it was due to backend performance limits, but when we ran a quick sanity test, it turned out that a recent UI update had modified the checkout process, breaking the automation scripts. Again, a simple sanity check could have saved them from chasing the wrong problem.

Why Sanity Testing Matters

From a CTO’s perspective, performance testing is not just about identifying bottlenecks — it’s about ensuring teams work efficiently and don’t waste resources on avoidable issues. Sanity testing acts as an early warning system, helping teams verify test environments, scripts, and configurations before investing time in full-scale load tests. 

By integrating sanity checks into the workflow, companies can:

1. Reduce time spent on debugging. A quick sanity test can help teams catch issues in minutes instead of hours or days.
2. Optimize resource allocation. Instead of running expensive full-load tests prematurely, sanity checks allow for a more strategic approach.
3. Improve confidence in test results. Ensuring the test scripts function correctly before execution leads to more reliable performance insights.

How to Approach Sanity Testing in Load Testing

Sanity testing in performance engineering is not about deep analysis but about quick validation. Here are three key principles I’ve found useful:

1. Run a light load first. Instead of jumping to high concurrency, start with a handful of virtual users to verify if key transactions execute as expected.
2. Check for functional breaks. Ensure scripts interact correctly with APIs, UI elements, and backend processes. A failed login or missing key response should be flagged immediately.
3. Validate response consistently. While full load tests focus on performance trends, sanity tests should catch anomalies like missing data fields, incorrect error codes, or abrupt session timeouts.

By embedding sanity testing as a routine pre-check, teams can prevent false alarms in load test results and streamline their performance engineering efforts.

Making Sanity Testing an Essential Part of Your Workflow

Sanity tests should be lightweight but reliable. A well-structured sanity check can be automated and integrated into CI/CD pipelines to validate test environments before major performance runs. It’s a simple yet effective way to ensure that your load tests don’t start on the wrong foot.

Sanity testing has saved me and my team countless hours over the years. If you’ve had similar experiences—whether cautionary tales or best practices — I’d love to hear your thoughts!

For a deeper dive into best practices and real-world scenarios, check out my blog post on sanity testing in load testing.