chigai-core

Modern visual regression testing with puppeteer and blink-diff

Visual regression testing

Visual regression testing: compare your current state against your baseline. It's nothing new. We've done this for ages. Comparing two images. Looking at the current version and the previous one. Searching for the difference. On our own. Manually.

Well, Chiagi does this automatically. It takes a screenshot from a given URI and compares it to the previous version.

Automated. Always

Chigai is designed to be used in your tests. You can use it in your favourite testrunner. As a regression tool. If your layout changes, it won't go on unnoticed.

How to use this?

Chigai-Core provides the core functionalities: The regression testing of a given url and creating a fresh reference item beforehand. Chigai-core is not meant to be used directly. Use the CLI or the API modules. They provide a clean facade for the core functions.

Regression testing

Provide a url and options such as the viewport width (default: 1024), viewport height (default: 720) or a threshold (default: 0.01 = 1%) for the image comparison. Chigai-core creates a new screenshot of the whole page and compares it to the last specified reference. If their difference is lower than the given threshold, matchwill be true. Otherwise, match becomes false.

Chigai creates a unique identifier from the url, the viewport size and the timeout.

API

Chigai-Core provides two public APIs:

regression(uri, options)

Handles the regression test for an items. Each item requires a property "uri" and can have an optional set of options. It returns an async function and finaly a return object.

reference(uri, options)

Creates a new reference for an item. Each item requires a property "uri" and can have an optional set of options. It returns an async function and finaly a return object.

Configuration options

Options can either be passed as arguments per call or globally via .chigairs.json file. The options-object takes precedence.

vw

Default: 1024. The with of the viewport you cant to screenshot. This will be part of the unique identifier.

vh

Default: 786. The height of the viewport you cant to screenshot. This will be part of the unique identifier.

threshold

Default: 0.01. The threshold to use for the comparison. This will not be part of the unique identifier.

path

Default: ./screenshots There's the possiblitly to pass a custom path to chigai. It's relative to your working directory. Use this to share your reference items (e.g. via source control, rsync ...).

wait

Default: 0. Wait this amount of miliseconds after the page's load-event before making the screenshot. This will not be part of the unique identifier.

.chigai.json

You can store project wide setttings in this file. It takes the same key-value-pairs as the options-object. Plus an additional path property.

{
	"path" : "./myscreenshots",
	"threshold": 0.5,
	"vw": 1200,
	"vh" : 800,
	"wait": 5000
}

Return Object

Each API returns an object with the following properties:

viewport

An object with two properties, width and height, indicating the viewport size of the screenshot.

uri

The screnshotted location

threshold

The threshold used for the comparison

wait

The delay between load and screenshotting

path

The path to the screenshots

timestamp_iso

An ISO-Timestamp of the screenshot

hash

The unique identifier of this screenshot. Based on the uri, viewport width, viewport height and wait

regression_item

The path to the regression item. The latest screenshot of this location.

reference_item

The path to the reference item. The reference screenshot of this location.

difference_item

The path to an image showing the difference between the reference and the regression item.

match

Boolean, true if the difference is below the threshold, aka "success".

screenshot

Boolean, true if the screenshotting of the current location was successful.

fresh

Boolean, true if this pass resulted in a fresh reference item: none available or forced.

Fresh reference

If you know you changed the layout, just set a new reference item before running the tests again.

Installation

$ yarn add chigai-core

Example

Chigai-core is not meant to be used directly. Use the CLI or the API modules. They provide a clean facade for the core functions.

Tech Stack

• ECMAScript 2018 on nodejs v8.5.0
• blink-diff v1.0.1
• fs-extra-plus v0.1.3
• puppeteer v0.11.0
• 100% code coverage using mocha v3.5.2, chai v4.1.2 and nyc v11.2.1,

Resources

• GoogleChrome/puppeteer - Headless Chrome Node API
• yahoo/blink-diff - A lightweight image comparison tool

License

Licensed under the MIT license.

Copyright (c) 2016, 2017 Martin Krause [email protected] http://martinkr.github.io)