Reference
Playwright

Load testing with Playwright and Artillery

Overview

Built-in since: v2.0.0-33

Playwright (opens in a new tab) is a modern browser automation framework by Microsoft. Artillery supports running Playwright-based scripts as load tests, including running Playwright at scale using AWS Fargate.

Features

→ See Why load test with headless browsers?

Current limitations

  • TypeScript support is available but experimental. See Example 3 below.
  • Only Chrome is available. Restricting the integration to just one browser improves startup time performance for large load tests and does not have any consequential effects on the results of load tests themselves.

Usage

The Playwright engine is built into Artillery.

Create a new Artillery script in hello-world.yml:

config:
  target: https://www.artillery.io
  # Load the Playwright engine:
  engines:
    playwright: {}
  # Path to JavaScript file that defines Playwright test functions
  processor: "./flows.js"
scenarios:
  - engine: playwright
    testFunction: "helloFlow"

Create a test function in flows.js:

(Note: this script was generated with playwright codegen (opens in a new tab). page is an instance of Playwright page (opens in a new tab).)

module.exports = { helloFlow };
 
async function helloFlow(page) {
  //
  // The code below is just a standard Playwright script:
  //
  // Go to https://artillery.io/
  await page.goto("https://www.artillery.io/");
  // Click text=Pricing
  await page.click("text=Cloud");
}

Run it:

artillery run hello-world.yml

Artillery will run the test and automatically record front-end performance metrics that measure perceived load speed (opens in a new tab) such as LCP and FCP:

--------------------------------
Summary report @ 11:24:53(+0100)
--------------------------------

vusers.created.total: ....................................... 1
vusers.completed: ........................................... 1
vusers.session_length:
  min: ...................................................... 5911.7
  max: ...................................................... 5911.7
  mean: ..................................................... 5911.7
  median: ................................................... 5944.6
  p95: ...................................................... 5944.6
  p99: ...................................................... 5944.6
browser.page.FCP.https://artillery.io/:
  min: ...................................................... 1521.1
  max: ...................................................... 1521.1
  mean: ..................................................... 1521.1
  median: ................................................... 1525.7
  p95: ...................................................... 1525.7
  p99: ...................................................... 1525.7
browser.page.LCP.https://artillery.io/:
  min: ...................................................... 1521.1
  max: ...................................................... 1521.1
  mean: ..................................................... 1521.1
  median: ................................................... 1525.7
  p95: ...................................................... 1525.7
  p99: ...................................................... 1525.7
browser.page.FCP.https://artillery.io/cloud/:
  min: ...................................................... 205.3
  max: ...................................................... 205.3
  mean: ..................................................... 205.3
  median: ................................................... 206.5
  p95: ...................................................... 206.5
  p99: ...................................................... 206.5
browser.page.LCP.https://artillery.io/cloud/:
  min: ...................................................... 205.3
  max: ...................................................... 205.3
  median: ................................................... 206.5
  p95: ...................................................... 206.5
  p99: ...................................................... 206.5

Configuration

The underlying Playwright instance may be configured through config.engines.playwright, as well as other options. The following configuration options are available:

NameValid OptionsDescription
launchOptionsPlaywright browserType.launch() (opens in a new tab) options objectConfigure the browser instance started by Playwright
contextOptionsPlaywright browser.newContext() (opens in a new tab) options objectConfigure browser contexts created for each virtual user
defaultNavigationTimeoutNumber (in seconds)Shorthand for setting setDefaultNavigationTimeout() (opens in a new tab) and setDefaultTimeout() (opens in a new tab)
extendedMetrics
  • false (default)
  • true
Report additional metrics.
aggregateByName
  • false (default)
  • true
Group metrics by scenario name rather than by URL.
showAllPageMetrics
  • false (default)
  • true
Send Web Vital metrics for all pages. By default, Artillery only displays Web Vital metrics for a URL that starts with the config.target URL. This avoids reporting metrics for third-party pages and iframes.
useSeparateBrowserPerVU

Added in: v2.0.4

  • false (default)
  • true
Use a separate browser for each VU (instead of a new browser context (opens in a new tab)). This will require a lot more CPU and memory and is not recommended for most tests.
testIdAttribute

Added in: v2.0.5

StringWhen set, changes the attribute used by locator page.getByTestId (opens in a new tab) in Playwright.

config.target as baseURL

Added in: v2.0.6

The config.target is automatically set as the baseURL (opens in a new tab) for the Playwright test. This means that you can use relative URLs (e.g. page.goto('/docs')) in your Playwright scripts, and they will be resolved relative to the config.target URL.

If you are not using relative URLs in your test script, full URLs will still work as usual.

Examples

Example 1: turn off headless mode

You can turn off the default headless mode to see the browser window for local debugging by setting the headless (opens in a new tab) option.

config:
  engines:
    playwright:
      launchOptions:
        headless: false

Notes:

  • When running tests in Fargate, headless mode is enabled by default, as you cannot run in Fargate without it.

    Added in: v2.0.5

Example 2: set extra HTTP headers

This example sets the extraHTTPHeaders (opens in a new tab) option for the browser context that is created by the engine.

config:
  engines:
    playwright:
      contextOptions:
        extraHTTPHeaders:
          x-my-header: my-value

Example 3: use TypeScript functions as test functions

Added in: v2.0.4

You can use a TypeScript file in config.processor.

config:
  target: https://www.artillery.io
  engines:
    playwright: {}
  processor: "./flows.ts"
scenarios:
  - engine: playwright
    testFunction: "helloFlow"
import { Page } from "playwright";
import { expect } from "@playwright/test";
 
export async function helloFlow(page: Page) {
  await page.goto("https://www.artillery.io/");
  await expect(page.getByText("Never Fail To Scale")).toBeVisible();
}

Known Limitations

  • TypeScript support is experimental and may not work in all cases.
  • One known case is that requiring the @playwright/test package to use features like expect will currently not work.

    Added in: v2.0.6

  • If you run into issues with particular npm packages, please read the Typescript custom code documentation.

Example 4: Aggregate metrics by scenario name

By default metrics are aggregated separately for each unique URL. When load testing the same endpoint with different/randomized query params, it can be hepful to group metrics by a common name.

To enable the option pass aggregateByName: true to the playwright engine and give a name to your scenarios:

config:
  target: https://artillery.io
  engines:
    playwright: { aggregateByName: true }
  processor: "./flows.js"
scenarios:
  - name: blog
    engine: playwright
    testFunction: "helloFlow"

flows.js:

module.exports = { helloFlow };
 
function helloFlow(page) {
  await page.goto(`https://artillery.io/blog/${getRandomSlug()}`);
}

This serves a similar purpose to the useOnlyRequestNames option from the metrics-by-endpoint plugin.

Test function API

Page argument

By default, only the page argument (see Playwright's page API (opens in a new tab)) is required for functions that implement Playwright scenarios, e.g.:

module.exports = { helloFlow };
 
async function helloFlow(page) {
  // Go to https://artillery.io/
  await page.goto("https://artillery.io/");
}

Virtual user context and events arguments

The functions also have access to the virtual user context, which can be used for several purposes:

  • Accessing scenario (and environment) variables for different virtual users (vuContext.vars);
  • Getting the current virtual user ID (vuContext.vars.$uuid);
  • Getting the scenario definition for the scenario currently being run by the virtual user (vuContext.scenario), including its name.

Additionally, the events argument can be used to track custom metrics.

module.exports = { helloFlow };
 
async function helloFlow(page, vuContext, events) {
  // Increment custom counter:
  events.emit("counter", `user.${vuContext.scenario.name}.page_loads`, 1);
  // Go to https://artillery.io/
  await page.goto("https://artillery.io/");
}

test.step argument

Added in: v2.0.0-38

The final argument of the function is test, which contains the step property. The API for test.step is similar to Playwright's own test.step, which allows you to re-use similar code. The purpose in Artillery is slightly different: to emit custom metrics that represent how long each step takes.

async function loginSearchAndLogout(page, vuContext, events, test) {
   //1. simply add this line to your scenario function, or use test.step below instead
  const { step } = test;
  const userid = vuContext.vars.userid;
  const recordid = vuContext.vars.recordid;
 
  //2. wrap any logic you have in steps (sometimes you might already have something like this done from existing playwright tests)
  await step("landing_page", async () => {
    await page.goto('https://internaltesturl.com/landing');
  })
 
  await step("submit_login", async () => {
    await page.getByLabel('id-label').fill( `${userid}` );
    await page.getByLabel('Password').fill(`${password}`);
    await page.getByRole('button', { name: 'Submit' }).click();
  })
 
  await step("search_record", async () => {
    await page.getByPlaceholder('enter request id').fill(`${recordid}`);
    await page.getByRole('button', { name: 'Go' }).click();
    await page.locator('css=button.avatar-button').click();
  })
 
  await step("logout", async () => {
    await page.getByText('Logout').click();
  })
}

The above code will now emit custom metrics for each step in addition to the default metrics:

browser.step.landing_page:
  min: ......................................................................... 87
  max: ......................................................................... 150
  mean: ........................................................................ 118.5
  median: ...................................................................... 89.1
  p95: ......................................................................... 89.1
  p99: ......................................................................... 89.1
browser.step.submit_login:
  min: ......................................................................... 300
  max: ......................................................................... 716
  mean: ........................................................................ 571.6
  median: ...................................................................... 561.2
  p95: ......................................................................... 561.2
  p99: ......................................................................... 561.2
browser.step.search_record:
  min: ......................................................................... 287
  max: ......................................................................... 801
  mean: ........................................................................ 544.6
  median: ...................................................................... 290.1
  p95: ......................................................................... 290.1
  p99: ......................................................................... 290.1
browser.step.logout:
  min: ......................................................................... 52
  max: ......................................................................... 334
  mean: ........................................................................ 193.1
  median: ...................................................................... 140.2
  p95: ......................................................................... 200.4
  p99: ......................................................................... 200.4

Metrics reported by the engine

In addition to the default metrics reported by Artillery, the Playwright engine reports the following metrics:

MetricTypeDescription
browser.http_requestsCounter

(count)

Number of HTTP requests made by all virtual users during this time period.
browser.page.codes.<code>

Added in: v2.0.4

Counter

(count)

Number of different HTTP status codes, e.g. browser.page.codes.200 is the number of 200 OK requests.
browser.page.TTFB.<page_url>.<aggregation>Histogram

(milliseconds)

Time To First Byte (opens in a new tab) (Web Vital metric) measurement for a specific page_url.
browser.page.FCP.<page_url>.<aggregation>Histogram

(milliseconds)

First Contentful Paint (opens in a new tab) (Web Vital metric) measurement for a specific page_url.
browser.page.LCP.<page_url>.<aggregation>Histogram

(milliseconds)

Largest Contentful Paint (opens in a new tab) (Core Web Vital metric) measurement for a specific page_url.
browser.page.FID.<page_url>.<aggregation>Histogram

(milliseconds)

First Input Delay (opens in a new tab) (Core Web Vital metric) measurement for a specific page_url (if available).
browser.page.INP.<page_url>.<aggregation>

Added in: v2.0.5

Histogram

(milliseconds)

Interaction to Next Paint (opens in a new tab) (Core Web Vital metric) measurement for a specific page_url (if available).
browser.page.CLS.<page_url>.<aggregation>Histogram

(shift score)

Cumulative Layout Shift (opens in a new tab) (Core Web Vital metric) measurement for a specific page_url (if available).

Extended metrics

If extendedMetrics is enabled, the following metrics are also reported:

MetricTypeDescription
browser.page.domcontentloadedCounter

(count)

Number of DOM Content Loaded (opens in a new tab) events across all pages.
browser.page.domcontentloaded.<page_url>Counter

(count)

Number of DOM Content Loaded (opens in a new tab) events for a specific page_url.
browser.page.dominteractive.<aggregation>Histogram

(milliseconds)

Measurement of time taken for DOM to become interactive (opens in a new tab), across all pages.
browser.page.dominteractive.<page_url>.<aggregation>Histogram

(milliseconds)

Measurement of time taken for DOM to become interactive (opens in a new tab), for a specific page_url.
browser.memory_used_mb.<aggregation>Histogram

(megabytes)

Measurement of usedJSHeapSize.

If test.step() API is used, the following additional histogram is reported:

  • browser.step.<step_name>.<aggregation> (milliseconds) - measurement of time taken for each step in the scenario.

Playwright compatibility

Since Artillery uses the playwright package to run the tests, the version of Playwright used by Artillery is important. The following table shows the compatibility between Artillery and Playwright versions:

Artillery versionPlaywright versionChromium version
2.0.6 (opens in a new tab)1.41.2 (opens in a new tab)121.0.6167.57
2.0.5 (opens in a new tab)1.41.0 (opens in a new tab)121.0.6167.57
2.0.4 (opens in a new tab) - 2.0.0-38 (opens in a new tab)1.39.0 (opens in a new tab)119.0.6045.9

Older versions of Artillery were not pinned to a specific Playwright package, so they are not tracked. It's advised to use one of the versions listed above.

Why load test with headless browsers?

Load testing complex dynamic web apps can be time consuming, cumbersome, and brittle compared to load testing pure APIs and backend services. The main reason is that testing web apps requires a different level of abstraction: whereas APIs work at API endpoint level, when testing web apps pages and user flows is a much more useful abstraction that maps onto how the web app is actually used.

Without Playwright

  • Figure out which HTTP APIs are used by the web page
  • Figure out what actions in the UI trigger calls to which APIs
  • Figure out what in-page JavaScript code does and how it interacts with the backend
  • Try to mimic realistic load on the backend at protocol level or by using HAR files
  • Ignore limitations with how dynamic such tests can be, and accept how brittle and time consuming maintetance is going to be

With Playwright

  • Just write UI-centric code and let the web app itself call the backend
  • Run lots of Playwrigth scripts to generate load on the backend

Testing HTTP APIs vs dynamic web apps

Ultimately, testing a backend HTTP API is very different from testing a web application that may use many such APIs and use client-side JavaScript to communicate with those APIs.

HTTP APIs & microservicesWeb apps
Abstraction levelHTTP endpointWhole page
Surface areaSmall, a handful of endpointsLarge, calls many APIs. Different APIs may be called depending on in-page actions by the user
Formal specUsually available (e.g. as an OpenAPI spec)No formal specs for APIs used and their dependencies. You have to spend time in Dev Tools to track down all API calls
In-page JSIgnored. Calls made by in-page JS have to be accounted for manually and emulatedRuns as expected, e.g. making calls to more HTTP endpoints