What is Concurrency Testing in Software Testing?

Concurrency is the term used when two or more events happen simultaneously. This is applicable to a system or software as well. The concurrency testing is conducted to understand how an application will respond when multiple users logged in at the same time. Generally, when multiple users perform the same action it often affects the application’s response time, eventually led to a crash. By running a concurrency test, testers can detect such crashes and make necessary changes to make the app more reliable for end users.

Concurrency is when more than one person downloads or stream the same file.

Example 1 – Two trains running on the same track or running on two tracks simultaneously can be considered as a perfect example of concurrency.

Example 2 – Most of us use Amazon to order products. Imagine a situation when multiple users logged in to the app or order the same product simultaneously. Such actions will more likely create some errors. This is where concurrency testing helps. It ensures all users can perform the same task at the same time without facing any difficulty.

What makes the application crash when multiple users multitask simultaneously?

A concurrent program runs simultaneously with another concurrent program. Each task executed shares some information with the system. Perform multiple tasks at the same time can change the sequence of execution, leading to incorrect results and repetition of errors. Concurrent testing helps in eliminating these errors.

Concurrency Testing Process

Below are the 5 steps involves in concurrency testing −

  • Creating the test plan
  • Analyzing the plan
  • Creating various scenarios and classifying them into high and low level

  • Developing an appropriate environment for the test

  • Testing the program by executing two or more tasks simultaneously.

You can perform concurrent testing with tools like LoadNinja, LoadRunner, Apache JMeter, etc.

The first step for concurrency testing is to create a rendezvous point using your testing tool. It helps in creating an intense user load on the server. The next step is to create a scenario by recording and enhancing the script. You can add concurrent users through the controller component if you are using LoadRunner. This feature may be named differently in other tools.

Now all users user must wait at the same point. In this case, all set to click the login button. To achieve a rendezvous point, all users have to click the button at the same time.

Concurrency Testing Techniques

Techniques used by testing engineers to run concurrency testing −

  • Code review − Reviewing the code is a time-consuming process that involves checking the embedded code and its structures.

  • Static analysis − It is a process to detect bugs in the system. It is conducted by checking and evaluating the coding system of the program before running the code.

  • Con Testing − It is executed to detect deficiencies in the unit testing process. It is also useful in removing synchronization faults in a multithreaded java program.

  • Reachability Testing − It is used to accumulate test sequences as the testing process progresses. Consequently, it helps is evaluate all behaviors of the program. However, it is impossible to run, especially when several applications are involved. It is still in the research phase. In the coming years, it has the potential to change the landscape of concurrency testing.

  • Fuzz Testing − It is conducted to find hackable software bugs, coding errors, and security loopholes by feeding random and unexpected data into a program.

  • Random Testing − In this process, the program is tested by generating random and independent inputs. In most cases, around five to ten threads are tested simultaneously.

Advantages of Concurrency Testing:

Reduces testing time and effort: Running a concurrency test helps in limiting the scope of concurrent interactions. Instead of testing all components, you can detect the components that require more testing. As a result, you can test an application without putting more effort into elements that hardly matters.

No need to review the entire code: With creating encapsulation value, which lets you analyze a specific portion of a program. Meaning, no need to analyze the whole coding structure of a program.

Increased reliability: A single application used by multiple users at a time can cause compatibility and stability issues. Concurrency testing helps in checking the reliability and robustness of the software, ensures it works concurrently.

Challenges in Concurrency Testing:

While concurrency testing is one of the most essential testing processes, it is not free from challenges −

  • Time-consuming − Undoubtedly concurrency testing can take a huge chunk of time. Although there are automation tools, the process still requires the constant attention of the developers.

  • New errors are introduced − Unlike most testing processes, concurrency testing doesn’t fix errors gradually as it progresses. Testers can still discover new errors while dealing will existing ones. That’s what makes it more exhausting.

  • Several platforms are required − An application or program nowadays is run on multiple devices. Therefore, you need to test them on different platforms.

  • Long waiting period − You have to wait for a long period for the results. The function return results through call-back functions or notifications instead of delivering them immediately.

  • Debugging is hard − Most defects found in this testing are time-bound and hard to reproduce, making the debugging process harder.


No doubt concurrency testing is a daunting affair with a high failure rate compared to sequential programming. However, considering the dynamic technological changes, and ever-growing user rates, it’s essential for an application to withstand heavy traffic without compromising user experience. Hence, the need for a concurrent program is very crucial in the internet era. Many researches have been conducted to make this process cheaper and time-efficient. This involves adapting existing techniques and developing new ones.

Updated on: 20-Aug-2021


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