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Basic Performance Testing Interview Questions And Answers

Introduction

Performance testing is a process of testing applications for non-functional requirements, which determines the application's speed, stability, responsiveness, and scalability under the stipulated workload. A system’s performance is one of the leading indicators to determine its performance in the market. Learn fundamentals of testing through our performance testing training and certification. 

Q1. Explain Performance Testing?

Ans- Performance testing intends to determine the responsiveness, reliability, throughput, interoperability, and scalability of a system and application under a given workload. It could also determine the speed or effectiveness of a computer, network, software application, or device. Testing can be conducted on software applications, system resources, targeted application components, databases, etc. It usually involves an automated test suite, as this allows for easy, repeatable simulations of various standard, peak, and exceptional load conditions. 

Such forms of testing help verify whether a system or application meets the specifications claimed by its vendor. The process can compare applications regarding speed, data transfer rate, throughput, bandwidth, efficiency, or reliability. Performance testing can also aid as a diagnostic tool in determining bottlenecks and single points of failure. It is often conducted in a controlled environment and in conjunction with stress testing, a process of determining the ability of a system or application to maintain a certain level of effectiveness under unfavorable conditions.

Q2. Why Are Performance Tests Conducted at High Levels?

Ans- At a very high level, performance testing is always conducted to address one or more risks related to expense, opportunity costs, continuity, or corporate reputation. Conducting such tests helps give insights into software application release readiness, adequacy of network and system resources, infrastructure stability, and application scalability, just to name a few. Gathering estimated performance characteristics of application and system resources before the launch helps to address issues early and provide valuable feedback to stakeholders, helping them make crucial and strategic decisions. Learn more about why performance testing is important. 

Q3. What Grounds Are Covered in Performance Testing?

Ans- Performance testing covers a whole lot of ground, including areas such as:

  • Assessing application and system production readiness
  • Evaluating against performance criteria
  • Comparing performance characteristics of multiple systems or System configurations.
  • Identifying the source of performance bottlenecks
  • Aiding with performance and system tuning
  • Helping to identify system throughput levels
  • Testing tool

Most of these areas are intertwined with each other, each aspect contributing to attain the overall objectives of stakeholders.

Q4. What Are The Core Activities in Performance Testing?

core activities

Ans- Understand the core activities in conducting performance tests:

  • Identify the test environment: Becoming familiar with the physical test and production environments is crucial to a successful test run. Knowing the environment's hardware, software, and network configurations helps derive an effective test plan and identify testing challenges from the outset. Usually, these will be revisited and revised during the testing cycle.
  • Identify acceptance criteria: What is the acceptable performance of the various modules of the application under load? Specifically, identify the response time, throughput, and resource utilization goals and constraints. How long should the end user wait before rendering a particular page? How long should the user wait to operate? Response time is usually a user concern, throughput a business concern, and resource utilization a system concern. Response time, throughput, and resource utilization are critical aspects of performance testing. Stakeholders usually drive acceptance criteria, and it is vital to continuously involve them as testing progresses, as the criteria may need to be revised.
  • Plan and design tests: Know the application's usage pattern (if any) and develop realistic usage scenarios, including variability among the various scenarios. For example, if the application has a user registration module, how many users typically register for an account daily? Do those registrations happen all at once, or are they spaced out? How many people frequent the landing page of the application within an hour? Questions such as these help to put things in perspective and design variations in the test plan. 
  • Prepare the test environment: Configure the test environment, tools, and resources necessary to conduct the planned test scenarios. Ensuring that the test environment is instrumented for resource monitoring is vital to help analyze results more efficiently. Depending on the company, a separate team might be responsible for setting up the test tools, while another may be responsible for configuring other aspects, such as resource monitoring. A single team is responsible for setting up all aspects in other organizations.
  • Record the test plan: Record the planned test scenarios using a tool. There are numerous testing tools available, both free and commercial, that do the job quite well, each having its pros and cons. Such tools include HP Load Runner, NeoLoad, LoadUI, Gatling, WebLOAD, WAPT, Loadster, LoadImpact, Rational Performance Tester, Testing Anywhere, OpenSTA, Loadstorm, etc. Some of these are commercial, while others are less mature or as portable or extendable as JMeter is. 
  • Run the tests: Once recorded, execute the test plans under light load and verify the correctness of the test scripts and output results. In cases where test or input data is fed into the scripts to simulate more realistic data (more on that in the later chapters), validate the test data. Another aspect to pay careful attention to during test plan execution is the server logs. This can be achieved through the resource monitoring agents set up to monitor the servers. It is paramount to watch for warnings and errors. A high rate of errors, for example, could indicate that something is wrong with the test scripts, application under test, system resource, or a combination of these.
  • Analyze results, report, and retest: Examine the results of each successive run and identify areas of bottleneck that need addressing. These could be system, database, or application-related. System-related bottlenecks may lead to infrastructure changes such as increasing the memory available to the application, reducing CPU consumption, increasing or decreasing thread pool sizes, revising database pool sizes, and reconfiguring network settings. Database-related bottlenecks may lead to analyzing database I/O operations, top queries from the application under test, profiling SQL queries, introducing additional indexes, running statistics gathering, changing table page sizes and locks, and more. 

Q5. What is The Relationship Between Performance Testing and Tuning?

Ans- A strong relationship exists between performance testing and tuning; one often leads to the other. Often, end-to-end testing unveils system or application bottlenecks that are regarded as incompatible with project target goals. Once those bottlenecks are discovered, the next step for most teams is a series of tuning efforts to make the application perform adequately.

Such efforts normally include but are not limited to:

  • Configuring changes in system resources.
  • Optimizing database queries.
  • Reducing round trips in application calls, sometimes leading to re-designing and re-architecting problematic modules.
  • Scaling out application and database server capacity
  • Reducing application resource footprint.
  • Optimizing and refactoring code; including eliminating redundancy, and reducing execution time.

Tuning efforts may also commence if the application has reached acceptable performance. Still, the team wants to reduce the system resources used, decrease the volume of hardware needed, or further increase system performance.

Q6. How Do You Define Baselines in Performance Testing?

Ans- Baseline is a process of capturing performance metric data for the sole purpose of evaluating the efficacy of successive changes to the system or application. It is important that all characteristics and configurations except those specifically being varied for comparison remains the same to make effective comparisons as to which change (or series of changes) is the driving result toward the targeted goal. Armed with such baseline results, subsequent changes can be made to the system configuration or application and testing results compared to see whether such changes were relevant or not. 

Some considerations when generating baselines include:

  • They are application-specific
  • They can be created for systems, applications, or modules
  • They are metrics/results
  • They should not be over-generalized
  • They evolve and may need to be redefined from time to time
  • They act as a shared frame of reference
  • They are reusable
  • They help identify changes in performance.

Q7. How is Load and Stress Testing Different from Performance Testing?

Ans- Load testing is the process of putting demand on a system and measuring its response, determining how much volume the system can handle. Stress testing is subjecting the system to unusually high loads far beyond its regular usage pattern to determine its responsiveness. These are different from performance testing, whose sole purpose is to determine the response and effectiveness of a system; that is, how fast the system is. Since load ultimately affects a system's response, performance testing is almost always done with stress testing. Want to know more about load testing? Check out the resources available online on load testing tutorials. 

Q8. What is a Test Plan?

Ans- Test Plan is the root element of the JMeter scripts and houses the other components, such as Threads, Config Elements, Timers, Pre-Processors, Post-Processors, Assertions, and Listeners. It also offers a few configurations of its own.

It allows you to define user variables (name-value pairs) that can be used later in your scripts. It also allows us to configure how the Thread Groups it contains should run; that is, should Thread Groups run one at a time? Several Thread Groups are often contained within a test plan as test plans evolve. This option allows you to determine how they run. By default, all Thread Groups are set to run concurrently. A helpful option when getting started is Functional Test Mode. When checked, all server responses returned from each sample are captured. This can prove helpful for small simulation runs, ensuring JMeter is configured correctly, and the server returns the expected results. 

Q9. Define Thread Groups in Performance Testing?

Ans- Thread Groups, as we have seen, are the entry points for any test plan. They

represent the number of threads/users JMeter will use to execute the test plan. All controllers and samplers for a test must reside under a Thread Group. Other elements, such as listeners, may be placed directly under a test plan in cases where you want them to apply to all Thread Groups or under a single Thread Group if they only pertain to that group. Thread Group configurations provide options to specify the number of threads that will be used for the test plan, how long it will take for all threads to become active (ramp up), and the number of times to execute the test. 

Each thread will execute the test plan entirely independently of the other threads. The ramp-up must be long enough to avoid a workload that is too large at the start of a test, as this can often lead to network saturation and invalidate test results. 

If the intention is to have X number of users active in the system, it is better to ramp up slowly and increase the number of iterations. A final option the configuration provides is the scheduler. This allows setting the start and end time of a test execution. For example, you can kick off a test for precisely 1 hour during off-peak hours.

Q10. What is The Purpose of Controllers in Performance Testing?

Ans- Controllers drive the processing of a test and come in two flavors: sampler controllers and logical controllers.

Sampler controllers send requests to a server. These include HTTP, FTP, JDBC, LDAP, and so on. Logical controllers, however, allow the customization of the logic used to send the requests. For example, a loop controller can repeat an operation several times; the if controller is for selectively executing a request, and the if controller is for continuing to execute a request until some condition becomes false. 

Q11. What is The Use of Samplers in Performance Testing?

Ans- Samplers are components that help send requests to the server and wait for a response. Requests are processed in the order they appear in the tree. Check out the following samplers:

  • HTTP Request
  • JDBC Request
  • LDAP Request
  • Soap/XML-RPC request
  • Web service (SOAP) request
  • FTP Request

samplers code

Each has properties that can be tweaked further to suit your needs. The default configurations are usually exemplary and can be used as is. Consider adding assertions to samplers to perform basic validation on server responses. During testing, the server may often return a status code of 200, indicative of a successful request, but fail to display the page correctly. At such times, assertions can help ensure the request was indeed successful.

Q12. What Are Logic Controllers?

Ans- Logic controllers help customize the logic to decide how requests are sent to a server. They can modify requests, repeat requests, interleave requests, control the duration of requests' execution, switch requests, measure the overall time taken to perform requests, and so on. 

Q13. What is The Purpose of Listeners in Performance Testing?

Ans- Listeners are components that gather the results of a test run, allowing it to be further analyzed. In addition, listeners can direct the data to a file for later use. Furthermore, they allow us to choose which fields to save and whether to use the CSV or XML format. All listeners save the same data, the only difference being how the data is presented on the screen. Listeners can be added anywhere in the test, including directly under the test plan. They will collect data only from the elements at or below their level.

Some listeners, such as Assert Results, Comparison Assertion Visualizer, Distribution Graph, Graph Results, Spline Visualizer, and View Results, in the tree are memory- and CPU-intensive and should not be used during actual test runs. They are okay to use for debugging and functional testing.

Q14. Why are Timers Valuable in Performance Testing?

Ans- By default, threads send requests without pausing between each request. You should specify a delay by adding one of the available timers to the Thread Group(s). This also helps make your test plans more realistic, as users couldn't send requests at that speed. The timer causes a certain amount of time before each sampler in its scope.

Q15. What are Assertions?

Ans- Assertions are components that allow you to verify responses received from the server. In essence, they allow you to verify that the application is functioning correctly and that the server is returning the expected results. Assertions can be run on XML, JSON, HTTP, and other responses returned from the server. Assertions can also be resource-intensive, so don't have them on for test runs.

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Q16. What Do You Understand by Pre-Processor and Post-Processor Elements?

Ans- As the name implies, a pre-processor element executes some actions before making a request. Pre-processor elements are often used to modify the settings of a request just before it runs or to update variables that aren't extracted from the response text. Post-processor elements execute some actions after a request has been made. They are often used to process response data and extract values from it.

 Pre-processor and post-processor elements

Conclusion

With the growing complexity of software applications, the demand for performance testers is likely to remain strong. Secure your place in the growing market with Performance Testing Training & Certification, which gives you an in-depth insight into software behavior during workload. You will learn how to check the software's latency and response time. You can also check whether the software application is efficient for scaling. The course gives you the strength to analyze the overall performance of an application under different types of loads.

In this blog on Performance Testing interview questions and answers, we have compiled a few of the most often-asked questions in job interviews for performance testing-based profiles. Going through these questions helps you to secure your dream job. 

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