@percy/core

What is @percy/core?

@percy/core is a core library for Percy, a visual testing and review platform. It allows developers to capture screenshots of web pages and compare them to baseline images to detect visual changes. This package provides the core functionality needed to integrate Percy into various testing frameworks and CI/CD pipelines.

What are @percy/core's main functionalities?

Initialize Percy

This code initializes a new instance of Percy, which is the first step in setting up visual testing for your project.

const Percy = require('@percy/core');
const percy = new Percy();

Capture a Snapshot

This code captures a snapshot of the specified URL. The snapshot is then compared to the baseline image to detect any visual changes.

await percy.snapshot('Home Page', { url: 'http://localhost:3000' });

Finalize Percy

This code finalizes the Percy session, uploading all captured snapshots for comparison and review.

await percy.finalize();

Other packages similar to @percy/core

cypress

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puppeteer

Puppeteer is a Node library that provides a high-level API to control Chrome or Chromium over the DevTools Protocol. It can be used for visual testing by capturing screenshots and comparing them, but it lacks built-in visual comparison features.

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README

@percy/core

The core component of Percy's CLI and SDKs that handles creating builds, discovering snapshot assets, uploading snapshots, and finalizing builds. Uses @percy/client for API communication, a Chromium browser for asset discovery, and starts a local API server for posting snapshots from other processes.

• Usage
  • #start()
  • #stop()
  • #idle()
  • #snapshot()
• Advanced
  • Download discovery browser on install
  • Skipping discovery browser download

Usage

A Percy class instance can manage a Percy build, take page snapshots, and perform snapshot asset discovery. It also hosts a local API server for Percy SDKs to communicate with.

import Percy from '@percy/core'

// create a new instance
const percy = new Percy(percyOptions)

// create a new instance and start it
const percy = await Percy.start(percyOptions)

Options

• token — Your project's PERCY_TOKEN (default process.env.PERCY_TOKEN)
• loglevel — Logger level, one of "info", "warn", "error", "debug" (default "info")
• server — Controls whether an API server is created (default true)
• port — API server port (default 5338)
• clientInfo — Client info sent to Percy via a user-agent string
• environmentInfo — Environment info also sent with the user-agent string
• deferUploads — Defer creating a build and uploading snapshots until later
• skipUploads — Skip creating a build and uploading snapshots altogether

The following options can also be defined within a Percy config file

• snapshot — Snapshot options applied to each snapshot
  • widths — Widths to take screenshots at (default [375, 1280])
  • minHeight — Minimum screenshot height (default 1024)
  • percyCSS — Percy specific CSS to inject into the snapshot
  • enableJavaScript — Enable JavaScript for screenshots (default false)
• discovery — Asset discovery options
  • allowedHostnames — Array of allowed hostnames to capture assets from
  • disallowedHostnames — Array of hostnames where requests will be aborted
  • requestHeaders — Request headers used when discovering snapshot assets
  • authorization — Basic auth username and password for protected snapshot assets
  • disableCache — Disable asset caching (default false)
  • userAgent — Custom user-agent string used when requesting assets
  • cookies — Browser cookies to use when requesting assets
  • networkIdleTimeout — Milliseconds to wait for the network to idle (default 100)
  • concurrency — Asset discovery concerrency (default 5)
  • launchOptions — Asset discovery browser launch options
    • executable — Browser executable path (default process.env.PERCY_BROWSER_EXECUTABLE)
    • timeout — Discovery launch timeout, in milliseconds (default 30000)
    • args — Additional browser process arguments
    • headless — Runs the browser headlessy (default true)

Additional Percy config file options are also allowed and will override any options defined by a local config file. These config file options are also made available to SDKs via the local API health check endpoint.

#start()

Starting a Percy instance will start a local API server, start the asset discovery browser, and create a new Percy build. If an asset discovery browser is not found, one will be downloaded.

await percy.start()
// [percy] Percy has started!

API Server

Starting a Percy instance will start a local API server unless server is false. The server can be found at http://localhost:5338/ or at the provided port number.

• GET /percy/healthcheck – Responds with information about the running instance
• GET /percy/dom.js – Responds with the @percy/dom library
• GET /percy/idle - Responds when the running instance is idle
• POST /percy/snapshot – Calls #snapshot() with provided snapshot options
• POST /percy/stop - Remotely stops the running Percy instance

#stop([force])

Stopping a Percy instance will wait for any pending snapshots, close the asset discovery browser, close the local API server, and finalize the current Percy build. When uploads are deferred, stopping the instance will also trigger processing of the upload queue. When force is true, queues are cleared and closed to prevent queued snapshots from running.

await percy.stop()
// [percy] Processing 3 snapshots...
// [percy] Snapshot taken: Snapshot one
// [percy] Snapshot taken: Snapshot two
// [percy] Snapshot taken: Snapshot three
// [percy] Uploading 3 snapshots...
// [percy] Finalized build #1: https://percy.io/org/project/123

await percy.stop(true)
// [percy] Stopping percy...
// [percy] Finalized build #1: https://percy.io/org/project/123

#idle()

This method will resolve shortly after pending snapshots and uploads have completed and no more have started. Queued tasks are not considered pending unless they are actively running, so deferred uploads will not be awaited on with this method.

percy.snapshot(...);
percy.snapshot(...);
percy.snapshot(...);

await percy.idle()
// [percy] Snapshot taken: ...
// [percy] Snapshot taken: ...
// [percy] Snapshot taken: ...

#snapshot(options)

Takes one or more snapshots of a page while discovering resources to upload with the snapshot. Once asset discovery has completed, the queued snapshot will resolve and an upload task will be queued separately. Accepts several different syntaxes for taking snapshots in various ways.

All available syntaxes will push snapshots into the snapshot queue without the need to await on the method directly. This method resolves after the snapshot upload is queued, but does not await on the upload to complete.

// snapshots can be handled concurrently, no need to await
percy.snapshot({
  name: 'Snapshot 1',
  url: 'http://localhost:3000',
  domSnapshot: domSnapshot,
  clientInfo: 'my-sdk',
  environmentInfo: 'my-lib'
})

// without a domSnapshot, capture options will be used to take one
percy.snapshot({
  name: 'Snapshot 2',
  url: 'http://localhost:3000',
  waitForTimeout: 1000,
  waitForSelector: '.done-loading',
  execute: async () => {},
  additionalSnapshots: [{
    name: 'Snapshot 2.1',
    execute: () => {}
  }]
})

// alternate shorthand syntax 
percy.snapshot({
  baseUrl: 'http://localhost:3000',
  snapshots: ['/', '/about', '/contact'],
  options: {
    widths: [600, 1200]
  }
})

// gather snapshots from an external sitemap
percy.snapshot({
  sitemap: 'https://example.com/sitemap.xml',
  exclude: ['/blog/*']
})

// start a server and take static snapshots
percy.snapshot({
  serve: './public',
  cleanUrls: true,
})

Options

When capturing a single snapshot, the snapshot URL may be provided as the only argument rather than a snapshot options object. When providing an options object, a few alternate syntaxes are available depending on the provided properties (see alternate syntaxes below).

Common options accepted for each snapshot:

• url — Snapshot URL (required)
• name — Snapshot name
• domSnapshot — Snapshot DOM string
• discovery - Limited snapshot specific discovery options
  • allowedHostnames, disallowedHostnames, requestHeaders, authorization, disableCache, userAgent

Common snapshot options are also accepted and will override instance snapshot options. See instance options for common snapshot and discovery options.

Capture options can only be provided when domSnapshot is missing:

• waitForTimeout — Milliseconds to wait before taking a snapshot
• waitForSelector — CSS selector to wait for before taking a snapshot
• execute — Function or function body to execute within the page before taking a snapshot
• additionalSnapshots — Array of additional sequential snapshots to take of the page
  • name — Snapshot name (required if no prefix or suffix)
  • prefix — Snapshot name prefix (required if no name or suffix)
  • suffix — Snapshot name suffix (required if no name or prefix)
  • waitForTimeout, waitForSelector, execute — See above

Alternate syntaxes

All snapshot syntaxes can be provided as items within an array. For example, a single method call can upload multiple DOM snapshots, capture multiple external snapshots, crawl a sitemap for snapshots, and host a local static server for snapshots.

Shared options accepted by all syntaxes:

• clientInfo — Client info to include with the build
• environmentInfo — Environment info to include with the build

The following alternate syntaxes may not be combined with snapshot options, but rather offer alternate methods for taking multiple snapshots.

List options can only be provided when a top-level snapshots is present:

• snapshots — An array of snapshot URLs or snapshot options (required)
• baseUrl — The full base URL (including protocol) used when snapshot URLs only include a pathname
• include/exclude — Include and exclude matching snapshot names
• options — Additional options to apply to snapshots
  • include/exclude — Include and exclude snapshots to apply these options to
  • Common snapshot and capture options (excluding url, domSnapshot)

Sitemap options can only be provided when a top-level sitemap is present:

• sitemap — The URL where an XML sitemap can be located (required)
• include/exclude — Include and exclude matching snapshot names
• options — Additional options to apply to snapshots
  • include/exclude — Include and exclude snapshots to apply these options to
  • Common snapshot and capture options (excluding url, domSnapshot)

Server options can only be provided when a top-level serve is present:

• serve — The static directory to serve relative to the current working directory (required)
• baseUrl — The base URL to serve the directory at, starting with a forward slash (/)
• cleanUrls — Set to true to strip .html and index.html from served URLs
• rewrites — A source-destination map for rewriting source URLs into destination pathnames
• snapshots — An array of specific snapshots to take while serving the static directory
• include/exclude — Include and exclude matching snapshot names
• options — Additional options to apply to snapshots
  • include/exclude — Include and exclude snapshots to apply these options to
  • Common snapshot and capture options (excluding url, domSnapshot)

Advanced

Download discovery browser on install

By default, the browser is only downloaded when asset discovery is started for the first time. This is because many features of the CLI do not require a browser at all, and automatically downloading a browser creates a much heavier footprint than needed for those features. However, if your CI caches dependencies after the install step, the browser will not be cached and will be downloaded every time Percy runs without it.

If the environment variable PERCY_POSTINSTALL_BROWSER is present and truthy, then the browser will be downloaded after the package is installed to allow it to be cached. You can also require @percy/core/post-install within another node module to trigger the browser download manually.

Skipping discovery browser download

If your CI comes with a Chromium binary pre-installed and you wish to skip Percy's own browser installation, you can set the respective discovery.launchOptions.executable config option. When the executable at the provided path exists, the default download will be skipped and the provided binary will be used instead. This option can also be set using the PERCY_BROWSER_EXECUTABLE environment variable.

Warning! Percy is only tested against the browser it downloads automatically. When providing a custom browser executable, you may experience unexpected issues.

How to update Chromium revision?

• Vist https://chromiumdash.appspot.com/releases?platform=Mac and check for current version in use.
• Get Branch Base Position for that release.
• Visit https://commondatastorage.googleapis.com/chromium-browser-snapshots/index.html?prefix=Mac/ and search for exact/neareast Branch Base Position.

Excerpt

check the release information on Github where the expected Chromium version and revision is specified.
For example:

v1.17.0
Big Changes
Chromium 76.0.3803.0 (r662092)

1. Go to Chromium browser snapshots

2. Choose the directory of your platform (e.g., Linux_x64)

3. Copy the revision number into the "Filter:" field without the "r" (e.g., 662092)

4. Fetch revision number for rest of the platform (Win, Win_x64, Mac, Mac_Arm), it should be nearby (Tip: verify the date of upload).