2023's IQCode: Frequently Asked JMeter Interview Questions and Answers

What is JMeter?

JMeter is an open-source load testing tool entirely built using Java programming language. The tool is widely used to load-test and measure the performance of different software products and applications. JMeter was initially designed for Web applications testing, but today it can be used to conduct other testing types like stress testing, load testing, and performance testing. The tool is often employed to test the performance of both dynamic and static assets along with web dynamic applications. Essentially, JMeter can help you simulate a heavy demand on a single server or a cluster of servers to test its strength or examine its overall performance under intense load scenarios.

It is important to note that JMeter is a protocol analyzer but not a browser. Although virtually, JMeter can behave like a browser - several web services and remote services, it doesn't undertake all the operations that browsers perform. For instance, JMeter doesn't run the JavaScript that exists in HTML pages. Similarly, it doesn't produce HTML pages like browser, and even though you can examine the answer as HTML, the timings aren't included in any samples, and only one sample from each thread is ever displayed at a time.

What are some of the key features of JMeter?

Here are some of the key features and functionalities of JMeter;

1. Ability to heavily load test servers, clusters, networks, and individual items.
2. Supports both dynamic and static resources along web dynamic applications testing.
3. It can perform a variety of performance tests, such as stress testing, load testing, and functional testing.
4. JMeter supports multiple protocols for diverse load testing scenarios.
5. Can be used for database server testing and various backend testing scenarios.
6. JMeter can aggregate and analyze test results in multiple ways.
7. Supports plugins for added extensions and customizations.

What is Distributed Testing?

Distributed testing refers to the process of running software tests on multiple devices or machines simultaneously. This type of testing is commonly used to test applications or systems in different environments and configurations. It allows testers to simulate real-world usage of software under different conditions and identify potential issues that could arise in different scenarios. Overall, distributed testing helps improve the quality and reliability of software products.

Setting Up Master-Slave Configuration in JMeter

To set up a master-slave configuration in JMeter, follow these steps:

1. Download and install JMeter on all the machines that will be used in the master-slave configuration.

2. On the machine that will act as the master, open JMeter and add the properties to the 'jmeter.properties' file as follows:

- Set the 'remote_hosts' property to the IP addresses of the slave machines, comma-separated.

- Set the 'client.rmi.localport' property to a unique number for each machine, starting from 1099.

3. On each slave machine, open JMeter and add the 'remote_start' property to the 'jmeter.properties' file with a value of 'true'.

4. Restart JMeter on all machines to apply the changes.

5. On the master machine, open the JMeter GUI and add a 'Distributed Test' element.

6. Specify the number of threads, loop count, and remote hosts in the 'Remote hosts' field.

7. Save the test plan and run it on the master machine.

8. The master machine will send the test plan to the slave machines, which will execute the tests and return the results to the master.

9. Once the test is complete, the master machine will aggregate the results from all the slaves and display them.

That's how you can set up a master-slave configuration in JMeter to distribute load testing across multiple machines.

Regular Expression Usage in JMeter and Difference between 'Contains' and 'Matches'

Regular expression is a powerful tool that is commonly used in JMeter to extract specific data from a response, such as a token or a session ID. Regular expressions are especially useful when dealing with dynamic data that changes with each request.

In JMeter, regular expressions can be used with various elements, including Regular Expression Extractor and Response Assertion. The Regular Expression Extractor element enables you to pick up the desired pattern from the server response using regular expressions, while the Response Assertion element uses regular expressions to check whether a specific pattern is present in the server response or not.

When using regular expressions in JMeter, there are two matching rules you can use – 'Contains' and 'Matches'.

'Contains' is used to verify if a particular text pattern is present in the server response. It matches the first occurrence of the pattern, regardless of what comes before or after it. For example, if we want to extract an authentication token from a server response that contains text like "authToken=12345", using 'Contains' rule we can search for the pattern "authToken=".

On the other hand, 'Matches' is used to verify if the server response matches a particular regular expression pattern. It provides finer-grained control over the matching process than 'Contains' rule. In our previous example, using 'Matches', we can create the regular expression pattern "\w{8}-\w{4}-\w{4}-\w{4}-\w{12}" to extract an authentication token of the format "12345678-abcd-efgh-ijkl-1234567890ab".

Therefore, when extracting data from server responses and validating specific patterns in JMeter, it is essential to understand the difference between 'Contains' and 'Matches' and use them appropriately based on your requirements.

Understanding Samplers and Thread Groups in JMeter

In JMeter, a Sampler represents a request that is sent to a server. Samplers are used to simulate user load on server and collect results. Thread Groups, on the other hand, are used to define the number of users (threads) and the duration of the test.

The Thread Group contains information such as the number of threads, ramp-up time, loop count, and duration. The ramp-up time defines how long it takes for JMeter to start all the threads. The loop count defines how many times the test should be repeated.

To simulate realistic user load, the Thread Group must be carefully configured. If the thread count is too low, the test may not accurately represent real-world scenarios. If the thread count is too high, it may overload the server and skew results.

Therefore, it is important to use appropriate thread groups and samplers to conduct accurate load testing in JMeter.

Types of Processors in JMeter

JMeter provides different types of processors that can be used to process the extracted data from the responses received from the server. Some of these processors are:

- Regular Expression Extractor: It extracts data by matching a regular expression pattern with the response data. - JSON Extractor: It extracts data from JSON responses. - XPath Extractor: It extracts data from XML responses by using XPath queries. - CSS/JQuery Extractor: It extracts data from HTML responses by using CSS or JQuery expressions.

Using the appropriate processor can help in handling the response data in a better way, making it easier to analyze and use for further testing purposes.

Order of Execution of JMeter Test Plan Elements

In JMeter, the test plan elements are executed in the following order:

1. Configuration Elements 2. Pre-Processors 3. Timers 4. Sampler 5. Post-Processors (unless SampleResult is null) 6. Assertions (unless SampleResult is null) 7. Listeners (unless SampleResult is null)

It is important to keep this order in mind when designing and building your JMeter test plan.

Configuration Elements in JMeter

In JMeter, Configuration Elements are used to define variables and settings that will be used by one or more samplers. These elements are executed before the sampler runs, and they allow you to modify the behavior of the sampler in various ways.

There are different types of Configuration Elements available in JMeter, including:

User Defined Variables:

Allows you to define variables that can be used throughout the test plan.

HTTP Cookie Manager:

Manages cookies for HTTP requests.

HTTP Header Manager:

Allows you to add or modify HTTP headers for requests.

HTTP Cache Manager:

Simulates browser cache by caching HTTP requests.

CSV Data Set Config:

Reads data from a CSV file and allows you to parameterize requests with this data.

LDAP Request Defaults:

Allows you to specify default settings for LDAP requests.

JDBC Connection Configuration:

Allows you to define a JDBC connection that can be used by one or more JDBC samplers.

By using Configuration Elements effectively, you can achieve more realistic and accurate load testing results in JMeter.

Various Data Parameterization Options in JMeter

JMeter offers several options for data parameterization. These include:

1. CSV Data Set Config: This allows test scripts to use external CSV files containing variable values, making it easy to parameterize data while avoiding the need to modify the script each time.

2. User Defined Variables: This feature enables users to define variables and their corresponding values within the test plan.

3. Random Variable: This generates random values for a given range of numbers.

4. Counter: This provides a sequential count of numbers, which can be useful for creating unique variable names.

5. Regular Expression Extractor: This allows testers to extract values from server responses using regular expressions.

6. XPath Extractor: This is similar to the Regular Expression Extractor, but uses XPath expressions.

By effectively using these data parameterization options, JMeter users can increase the flexibility of their tests and make them more efficient.

Assertions in JMeter

In JMeter, assertions are used to verify if the response of a request matches the expected result. They help in ensuring the correctness of the response and catching errors or bugs in the application.

For example, if the expected result of a request is to return a certain text or status code, an assertion can be added to verify if the response contains that text or returns the expected status code.

There are various types of assertions available in JMeter such as Response Assertion, Duration Assertion, Size Assertion, etc. Each type of assertion matches a specific criteria to verify the correctness of the response.

By adding assertions in JMeter, we can ensure that our application is functioning correctly and delivering the expected results.

Maximum Number of Threads on a Single System

What is the recommended maximum number of threads that should be allowed on a single system?

Comparison of Gaussian and Poisson Timers

When it comes to timers, two commonly used types are Gaussian and Poisson. Gaussian timers are used in situations where time intervals occur with a continuous and consistent probability distribution. On the other hand, Poisson timers are used when events occur randomly and independently of each other.

Gaussian timers are based on the Gaussian distribution, also known as the normal distribution, which is characterized by a bell curve. This type of timer is commonly used in systems that require precise control, such as in electronics or physics experiments. For example, when measuring the time it takes for a particle to travel a certain distance, a Gaussian timer would be used to ensure accurate results.

Poisson timers, on the other hand, are based on the Poisson distribution and are used when events occur randomly, such as in traffic flow or the arrival of customers at a store. These timers are useful in modeling processes where the occurrence of an event is independent of any previous events.

In conclusion, while both Gaussian and Poisson timers have their uses, the choice of which one to use depends on the specific application and the nature of the process being timed.

Purpose of Correlation in JMeter

Correlation is a process of extracting dynamic data from server responses and using it in subsequent requests. In JMeter, correlation is necessary when the server generates a unique value in response to each request that needs to be passed along to the next request. The purpose of correlation is to ensure that each subsequent request is unique and accurate, avoiding errors and inaccuracies in the test results. For example, if a user logs in and receives a session ID in the response, that session ID needs to be extracted and used in subsequent requests to simulate a real-world scenario.

Types of Listeners in Programming

In programming, there are different types of listeners, such as:

1. Action Listeners - used for detecting user actions like button clicks, menu selections, and keystrokes. 2. Mouse Listeners - used for detecting mouse-related events like clicks, movements, and drags. 3. Key Listeners - used for detecting keyboard events like key presses and releases. 4. Focus Listeners - used for detecting focus-related events like when a component gains or loses focus. 5. Window Listeners - used for detecting window-related events like when a window is opened or closed.

Understanding these listeners is important in creating responsive and interactive user interfaces in programming.

What is a workbench?

A workbench is a piece of furniture or a table designed for manual work or other professional activities like woodworking, metalworking, crafting, or electronics. It typically has a flat surface and places to store tools, making it an ideal workspace for various tasks. Workbenches are available in a wide range of sizes and styles, and some may have features like additional storage, built-in lighting, and adjustable height.

Explaining the Functioning of a Test Script Recorder

A test script recorder is a tool used for automating test cases. It works by recording user actions, such as mouse clicks and keyboard inputs, during a manual testing process and then plays back those actions to automate the execution of the test cases.

The working of the test script recorder involves the following steps:

1. Launch the test script recorder and start the recording process.
2. Perform the manual test steps that are required for the test case.
3. The recorder will capture the user actions and generate scripts that represent the steps performed.
4. Save the generated test scripts in a location and use them for future test executions.
5. When executing the automated test scripts, the recorder will replay the recorded actions to complete the test steps.
6. The tool will compare the expected and actual results to determine whether the test case has passed or failed.

Overall, the use of a test script recorder offers a considerable advantage for teams looking to accelerate their testing process and reduce the possibility of human error.

// Sample use of a test script recorder tool to automate test cases

Protocols Supported by JMeter

JMeter supports a wide range of protocols. Some of the protocols that JMeter supports are:

• HTTP/HTTPS
• FTP
• JMS
• LDAP
• SMTP
• TCP
• WebSocket
• SOAP
• POP3

JMeter can be used to test the performance of a variety of applications that use these protocols.

JMeter Variable and Function Syntax

JMeter provides variables and functions to manipulate and generate values during test execution. Variables hold dynamic data whereas functions generate or manipulate that data. The syntax for variables is "${variable_name}" and for functions, it is "${function_name(parameter)}".

Example of using a variable: - Define a variable as "base_url" with a value of "http://example.com" - To use this variable in an HTTP request, the syntax would be "${base_url}/endpoint".

Example of using a function: - Use the __time function to generate a timestamp in a specific format. Syntax: "${__time(ddMMyyyyHHmmss)}" - This will generate a timestamp in the format "ddMMyyyyHHmmss" (e.g. 31032021143025).

Functions can be chained together to create more complex data manipulations. For example: - "${__groovy(${__time(), } + 3600 * 1000,)}" will generate a timestamp one hour in the future.

In summary, JMeter variables and functions provide powerful capabilities to create dynamic test scenarios and to manipulate test data during test execution.

JMeter Interview Questions for Experienced

19. Can JMeter be used to record actions on a mobile device? If yes, what would be the process to do it?

Yes, JMeter can be used to record actions on a mobile device. The process to do it is as follows:

1. Set up a proxy server on a computer that will be used to connect to the internet.

2. Configure the mobile device to connect to the internet through the proxy server.

3. Start JMeter’s proxy server and configure the browser on the mobile device to use it.

4. Perform the actions on the mobile device that you want to record.

5. Stop the JMeter proxy server.

6. JMeter will create a script for the recorded actions, which can then be edited and run in JMeter.

By following this process, we can use JMeter to record actions on a mobile device and create scripts for load testing purposes.

Reasons for Recommending Running JMeter in Non-GUI Mode

Running JMeter in Non-GUI mode is highly recommended for various reasons:

 
- It consumes less memory as compared to the GUI mode.
- It improves the overall performance and makes JMeter run faster.
- It allows running tests in the background, without occupying the current terminal session.
- It enables running JMeter on remote servers without requiring a GUI environment.
- It generates test results in non-interactive mode, which can be easily parsed by external tools and plugins.
 

Performing Spike Testing with JMeter

To perform Spike Testing with JMeter, follow these steps:

1. Launch JMeter and create a new test plan. 2. Add the necessary Thread Group and other required elements. 3. Configure the Thread Group to set up the desired number of users and ramp-up period. 4. Add a Constant Throughput Timer and configure it to maintain the desired throughput rate. 5. Add all the required Samplers and listeners to your test plan. 6. Set up monitoring tools to monitor CPU and memory usage during the test. 7. Start the test and monitor the results.

Note that Spike Testing is best used for testing scenarios where there are sudden spikes in user traffic. It is important to closely monitor system performance during the test to identify and address any issues that may arise.

Using JMeter to Run Selenium Scripts

Yes, it is possible to use JMeter to run Selenium scripts. This can be achieved through the WebDriver Sampler plugin in JMeter.

To do this, follow these steps:

1. Download the WebDriver Sampler plugin from the JMeter Plugins Manager. 2. Set up your Selenium script as you normally would. 3. Add a WebDriver Sampler to your JMeter test plan. 4. Copy and paste your Selenium script into the WebDriver Sampler. 5. Run the test plan.

By using JMeter to run your Selenium scripts, you can benefit from the load and performance testing features that JMeter offers. This allows you to test the performance of your web application with simulated user traffic, and identify any bottlenecks or performance issues.

Handling Sessions and Cookies in JMeter

In order to handle sessions and cookies in JMeter, you can use the following steps:

1. Add a "HTTP Cookie Manager" to the Test Plan. 2. Configure the "User Defined Variables" to store the session ID and other relevant information. 3. Use regular expression extractors to extract session ID from HTTP responses. 4. Use the session ID variable wherever required in subsequent requests.

By using these steps, JMeter will be able to handle sessions and cookies in your test plan.

Crucial Steps in JDBC (Java Database Connectivity) Request Testing Process

When testing JDBC requests, some crucial steps should be followed:

1. Establish a JDBC connection with the database using the appropriate driver.
2. Create SQL statements to interact with the database.
3. Execute the SQL statements and retrieve the results.
4. Verify that the results retrieved match the expected results.
5. Test the application's behavior under different database conditions, such as when the database is inaccessible or when the request returns a large amount of data.

By following these steps, you can ensure that the JDBC requests are working as intended and that the application is able to interact with the database in a reliable and effective manner.

What is BeanShell Scripting?

BeanShell scripting is a lightweight scripting language that runs on the Java Virtual Machine (JVM). It provides support for dynamic language features such as loose typing and automatic object binding. BeanShell scripts can be used to extend the functionality of Java applications or to automate tasks. The syntax of BeanShell scripting is similar to Java, making it easy for Java developers to learn and use.

Code to write JMeter variable data to a CSV file:

The following code can be added to a JSR223 Sampler in JMeter to write the data stored in a JMeter variable to a CSV file:

import org.apache.jmeter.services.FileServer;
import java.io.File;
import java.io.FileWriter;

String varData = vars.get("variableName"); // Replace "variableName" with the name of your variable
File file = new File(FileServer.getFileServer().getBaseDir(), "output.csv");
boolean fileExists = file.exists();

FileWriter writer = new FileWriter(file, true);
if (!fileExists) {
   writer.write("Variable Data"); // Header for the CSV file
}

writer.write("\n" + varData); // Add variable data to the CSV file
writer.close();

Ensure that the variable name is replaced with the name of your actual variable. This code retrieves the value of the variable and appends it to a CSV file located in the JMeter FileServer directory. The first time the code runs, it adds a header to the file. The FileWriter is closed to release the file for other operations.

Understanding Root Certificate Authority (CA) Certificates

A root certificate authority (CA) certificate is a digital certificate used to verify the authenticity of other digital certificates issued by the same CA. It is the top-level certificate in a public key infrastructure (PKI) hierarchy, and it is used to sign other certificates. Root CA certificates are widely trusted and installed in web browsers, operating systems, and other software, making them an essential component of secure online communication. Without them, users would have to manually verify the trustworthiness of each website or service they access, which is not practical or efficient.

Factors that Influence the Number of Threads to Generate per System

There are multiple factors that can determine the ideal number of threads to generate in a system. Some of these factors include:

- The type of task being performed

- The amount of available resources (e.g. CPU, memory)

- The number of cores in the processor

- The complexity and size of the data being processed

In order to determine the optimal number of threads to generate, it is important to consider these factors and to test different thread configurations to find the one that provides the best performance.

Top Plugins Supported by JMeter

JMeter supports a wide range of plugins that extend its functionality and improve its performance testing capabilities. Some of the most significant plugins include:

- Ultimate Thread Group
- Throughput Shaping Timer
- JSON Plugins
- HTTP/2 Plugin
- Custom Thread Groups
- WebDriver Sampler
- DNS Cache Manager
- PerfMon Metrics Collector
- Apache Kafka Plugin
- HTML Report

These plugins enable JMeter to simulate various aspects of real-world scenarios and provide valuable insights into application performance.

JMeter Controllers

In JMeter, there are different types of controllers that can be used to control the user flow during load testing. These are:

1. Thread Group

: It is the starting point of any JMeter test plan, and controls the number of users and iterations for the test.

2. Logic Controllers

: These are used to manage the order in which requests are sent by the virtual users. Some of the commonly used logic controllers are If, While, Switch, Loop, etc.

3. Sample Controllers

: These are used to group and organize related requests within a test plan. Some of the examples of Sample Controllers are Simple Controller, Once Only Controller, and Throughput Controller.

4. Module Controllers

: These are used to integrate test modules, like scripts or recordings, into a test plan.

5. Test Fragments

: These are used to define reusable test components that can be shared across multiple test plans.

It is important to choose the appropriate controller based on the testing scenario to effectively simulate user behavior during load testing.

Differences between Ultimate Thread Group and other Thread Groups

The Ultimate Thread Group is different from other Thread Groups in several ways. One of the most significant differences is that the Ultimate Thread Group provides more extensive and flexible options for load testing. Additionally, the Ultimate Thread Group is designed to simulate different types of user behavior, making it more suited to complex testing scenarios.

Another difference is that the Ultimate Thread Group is more performance-oriented, allowing users to adjust thread parameters to maximize their system utilization. Other Thread Groups typically have more limited options in this regard.

Finally, the Ultimate Thread Group is more user-friendly, with a more intuitive interface that makes it easier for users to create and manage their load tests. Overall, the Ultimate Thread Group is a powerful tool for load testing that offers distinct advantages over other Thread Groups.