JMeter

JMeter is a web application load testing tool written in Java. Tests can be built either using the UI or directly in XML.

Concepts

Test Plans are the root of a project. They determine execution order of Thread Groups (the default is to run both concurrently) and whether generated data should be stored on-disk.
- Thread Groups create and manage lifetime of threads that serve as virtual users according to a specified ramp-up period and execute scenarios in them.
  - Controllers either generate traffic or perform some logical operation:
    - Samplers (also known as Generative Controllers) generate and send requests to a server and wait for a response.
      - Assertions ensure correctness of a request or response
      - Pre Processors execute before the sampler's request, e.g. to generate test data.
      - Post Processors execute after the sampler's request, e.g. for value extraction.
    - Logic Controllers determine which request (contained within them) should be executed next.
    - Test Fragments are a special type of controller that's only executed if referenced by an Include or Module Controller.
  - Timers introduce delays before executions to simulate user behaviour (e.g. reading, completing a form).
  - Listeners allow accessing gathered test case data.

Scoping is based on an element's location in the tree.

Elements aren't executed in the order of their definition:

Functions can be called in text inputs, and can be called with the syntax __funcName([arg1[, arg2]]).

Random(min, max)
Scripting:
- groovy(expr, varName) allows executing p.r.comp.lang.groovy (Private) code, storing the result in the named variable.
- javaScript(expr, varName) allows executing p.r.comp.lang.js (Private) code, storing the result in the named variable.
- jexl(expr, varName) executes a JEXL query.

DNS Cache Manager determines how DNS queries are served (via the host's DNS resolver, specified resolvers or statically) and how the values are cached.
HTTP Request Defaults reduces duplication by extracting common HTTP request values into a single element.
HTTP Header Manager allows specifying request headers.
HTTP Cookie Manager provides a per-thread cookie jar.
HTTP Cache Manager provides some emulation of browser Cache-Control header handling.

GraphQL HTTP Endpoint executes a GraphQL query or mutation.
HTTP Request fetches the given URL and can optionally fetch embedded resources matching the specified RegEx.
FTP Request performs an operation against an FTP server.
Flow Control Action allows performing thread or test flow control, useful when paired with logic controllers.

Simple Controllers may be used to visually group related samplers and controllers.
Transaction Controllers can be used to generate an additional sample combining samplers' timings to represent a single user-facing operation.
If Controllers execute their nested controllers if a given JavaScript expression evaluates to true.
While Controllers execute their children until the condition evaluates to false. There are three types of condition:
- "" exits the loop when the last sample in the loop fails.
- "LAST" performs as "", and will additionally not enter the loop if the sample immediately before the controller fails.
- Otherwise evaluate the expression and enter the loop only if its result is equal to "false".
Runtime Controllers loop over their children until the specified runtime is met.
Interleave Controllers iteratively execute only one of their children on each invocation. They can be configured to interleave across threads.
Random Order Controllers randomly select one of their children to execute on each invocation.
Once Only Controllers execute only once per thread and are subsequently skipped.
Include Controllers allow inclusion of Test Fragments from another JMeter Test Plan.
Module Controllers allow inclusion of Test Fragments from the current JMeter Test Plan.
Critical Section Controllers limit execution of their children to just one thread at a time.

JSR223 executes a JSR 223 script.
User Parameters assigns properties statically for the specified users.
HTML Link Parser extracts links and forms from HTML.
RegEx User Parameters extracts key-value pairs from the response as returned in regular expression match groups.

JSR223 executes a JSR 223 script.
CSS Selector Extractor extracts the value of the specified HTML attribute from an element matching the specified p.r.comp.lang.markup.css (Private) selector.
JSON Extractor extracts data from JSON responses using JSONPath expressions.
JSON JMESPath Extractor extracts data from JSON responses using JMESPath expressions.
XPath Extractor extracts XML/SGML elements using XPath expressions.
Regular Expression Extractor extracts text from a response using PCRE.

Constant Timers insert a constant delay between samplers.
Constant Throughput Timers wait for the sum of a minimum constant delay and a maximum random value (specified in milliseconds).
Synchronising Timers are designed to execute many requests at the same time, and work by blocking threads until the specified number of user threads are blocked.
Uniform Random Timers pause threads for a random amount of time, equally weighting all possible wait times.