What Is Performance Testing? Improving Stability and Reliability of Your App

Testing is an integral part of the development process as it helps ensure quality, security, and usability of software. One of its most important types is performance testing, aimed at evaluating how well your system performs in various conditions. 

So, what is performance testing? How exactly do you carry it out and what metrics are you paying attention to during the process? Read below to find out.

What Is Performance Testing? Improving Stability and Reliability of Your App

What is performance testing?

The performance testing meaning can be defined as a method that helps evaluate speed, responsiveness, stability, and reliability of a software application. The main goal of the process is to ensure the quality of the app and its seamless functioning in various conditions. Since you cannot predict the exact load volume that might occur, performance testing helps prepare the software for future load spikes and guarantee its failure-free operation even during extreme loads.

In addition to double-checking the quality of performance, this method also helps identify the most common performance issues and bottlenecks, such as:

  • Long load time: sometimes an app takes too long to load and that greatly impacts user experience;
  • Low response time: a low response time means a user has to wait to get a response from the app. Same as with long load time, low response time impacts user experience negatively.
  • Low scalability: the app cannot handle the growing load and cannot scale correspondingly, which results in failures.
  • Low throughput: a system cannot handle concurrent requests efficiently and thus, the data is transferred slower than needed;
  • Memory leaks: the consumed memory is not released properly, which leads to poor performance and potential system failures.
  • Database bottlenecks: occur with too slow database queries or with wrong indexing.
  • CPU bottlenecks: the CPU reaches its maximum capacity and cannot effectively execute tasks, thus impacting the performance.

Why performance testing is important

After understanding the performance testing definition, let’s look at its main benefits. Performance testing in software testing helps detect any existing issues and eliminate the factors that negatively affect the performance of the app. However, it’s not the only reason why organizations decide to conduct this process:

  • Preventing system’s failures and downtime: performance testing is a great proactive measure that helps address existing issues and vulnerabilities in advance and timely eliminate them, thus making the system more stable and robust.
  • Preparing for growth: if you plan to scale your app, this method is a highly effective way to check how ready the app is for future growth and what should be optimized to help it scale in a painless way.
  • Running software diagnostics: with the help of performance testing, organizations can regularly check their software and what kind of bottlenecks are to be eliminated.
  • Verifying the vendor’s claims: in order to check whether the system meets the stated specifications, organizations often run performance tests.
  • Collecting information for stakeholders: the results of performance tests are often presented to stakeholders as a proof of software’s stability and reliability.
  • Improving user experience: modern users expect their software products to be highly responsive and swift. So if an app does not meet these requirements and takes too long to load or respond, users will most likely abandon it. Needless to say that decreased user engagement has a direct and negative impact on a business.

Whatever reason you have for conducting performance testing, remember that the process requires a well-planned approach and several preparatory steps – we’ll talk about them in detail a bit later. For now, let’s look at the types of performance testing that are available for consideration.

The main types of performance tests

In order to accurately estimate the app’s performance in specific conditions, you need to emulate these conditions – this is where different methods come in. While there are two main types (load and stress testing), there are several of their variants that organizations use, depending on their specific business needs.

Load testing

This testing type evaluates how well a system performs under a specific (and anticipated) load by simulating the needed number of concurrent users and/or transactions. In this way, developers can identify potential bottlenecks that stop the system from scaling and implement needed optimizations. An interesting thing about load testing is that it can be applied to specific functionalities (i.e., a checkout) since for some parts of the app stellar performance and high responsiveness are critical.

Stress testing

Stress testing is aimed at evaluating the system’s performance under extreme and unexpected load volumes. In this way, developers estimate the app’s capacity limit and determine the breaking point where the system can no longer perform effectively. In addition to defining the app’s maximal capacity, stress testing also helps understand how long it will take the app to recover and what resources (CPUs, memory) are used the most.

There are two subsets:

  • Soak testing (endurance testing): the number of users (the load volume) increases gradually;
  • Spike testing: the number of users increases suddenly.

Scalability testing

This technique, as the name implies, tests the app’s ability to scale up and down in correspondence with the changing number of users. During this process, the number of users is specified and does not usually go beyond maximal limits. One of the biggest advantages of scalability testing is that it helps better plan the capacity addition for further performance improvement.

Capacity testing

Capacity testing is also aimed at estimating how well the app handles a specific number of users. The main difference here is that capacity testing estimates whether the system effectively handles the load that it was designed to. So in capacity testing you do not really go beyond the expected maximum – instead, you test the app’s capacity and whether anything prevents it from effective functioning.

The main metrics to consider and measure

There is a great variety of metrics that are usually measured and evaluated during the performance testing. Below, we list several examples:

  • Latency: the delay between the request initiation and the received response; 
  • Response time: the time it takes for a system to respond to a user’s request;
  • Throughput: the rate at which the application processes transactions or requests per unit of time;
  • Error rate: the percentage of requests that result in errors or failures;
  • Bandwidth: the volume of data (bits per second) that moves between workloads;
  • Memory: the amount of storage space available for a processor;
  • CPU interrupts per second: a number of interrupts a processor gets per second;
  • Peak response time: the longest time a system needs to respond while being under the peak load;
  • Session amounts: the maximum number of active sessions that can be open at once;
  • Average load time: the average amount of time it takes for a request to be delivered.

As you can see, most of the metrics revolve around the speed of a system’s response and the time it needs. Naturally, the faster the system responds, the better the user experience is. 

Performance testing process

While every software project is individual and hence requires an individual approach, there are several core performance testing stages that are to be included in every performance testing approach.

Definition of objectives and requirements

First, it is important to define clear requirements towards the testing process and establish objectives that you want to achieve. This includes understanding the expected load and defining thresholds and important metrics.

Creation of a test plan

Next, the testing team designs a test plan that normally describes the testing strategy, defines the testing environment, success criteria, and various test scenarios. By preparing a detailed test plan in advance, you ensure that your further activities will align with the business objectives and will help measure the right metrics.

Design of test scenarios

Think of test scenarios as of simulations of real-world user interactions with the system. In this way, a test scenario includes a set of actions that a user might perform and covers multiple aspects, like peak load, stress conditions, etc. This is needed to identify how an app performs in both expected and unexpected conditions. 

Configuration of test environment

Since testing does not happen in the production environment, you need to mirror it in the testing environment by properly configuring the latter. This includes configuration of hardware and software as well as network.

Execution of tests

Once everything is ready, the testing team performs the tests. The process includes the application of the simulated load and measurement and collection of defined metrics. This is important so the team later analyzes the system’s performance, assembles a report and, based on that, performs retesting.

Results analysis

As already mentioned, during the execution of tests, the team monitors real-time results and collects them. This data is then thoroughly analyzed to identify the bottlenecks and areas for improvement. 


Once the defined improvements are implemented and the system is analyzed, the team performs retesting to see whether optimization indeed addressed the existing issues. Some of the activities involved in optimization often include changes in code, configuration tweaks, or augmentation of the infrastructure. 

Reporting and creation of documentation

After the system is retested and its performance meets all needed criteria, the team creates an extensive report where it summarizes key findings and provides recommendations for further optimization. The creation of documentation is very important as it helps monitor changes in the system behavior and serves as a source of truth for any further activities, while also adding transparency to the internal processes.

Final word

Now that we’ve answered the “what is performance testing?” question, it’s clear that performance testing is a highly effective method for understanding how your app performs and what can be improved. However, it is important to accurately design the tests and prepare everything in advance so that the testing process brings benefits, not additional challenges.

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