Intern Visual Regression Testing

This project adds support for visual regression testing in Intern.

Overview

A visual regression test compares a screenshot of a webpage with a previously generated baseline providing the ability to make automated comparisons against a known-good version to ensure nothing has changed.

These tests can help engineers

• ensure a page is rendered identically on various browsers
• identify when a css change has an undesired effect elsewhere
• put a quick set of visual tests around legacy code to identify regressions

Installation

The intern-visual package should be installed as a peer of Intern

$ npm install intern intern-visual

Quick Start

Ok! You want to see all the great things Visual Regression Testing can do and how to do it! See real test code by looking in the tests/visual directory.

To run our visual regression tests

1. clone this project
2. install some tools npm install -g grunt-cli
3. npm install
4. start selenium
5. grunt test

APIs and Architecture

This Intern plugin can be broken down into three main pieces of functionality. The assertion layer is made up of assert and test; they provide a programmatic and configuration based approach, respectively. The comparison layer is used by the assertion layer to identify differences between the baseline and snapshot images. And the reporting layer is used by Intern to generate HTML reports.

assert

assert is a module that allows you to compare two sets of images (a baseline and snapshot). It is also responsible for generating baselines as necessary for future test runs. The method is called during functional testing like this:

import assertVisuals from 'visual/assert';

registerSuite({
    test() {
        this.remote()
            .get('https://sitepen.com')
            .setWindowSize(1024, 768)  // set the window size
            .takeScreenshot()
            .then(assertVisuals(this, {
                missingBaseline: 'snapshot'
            }));
    }
})

There are a number of options that can be passed to assert or set globally. The complete list of options can be seen in the module.

baseline: explicitly point to a baseline png to use. When this is not defined the test name is used to generate a path to a baseline

regenerateBaselines: when set to true, a new baseline will be automatically generated

test

test provides a wrapper around the assert module that will create a visual regression test from configuration.

import visualTest from 'visual/test';

registerSuite({
	test: visualTest({
		url: 'https://sitepen.com',
		width: 1024,
		height: 768,
		missingBaseline: 'snapshot',
	});
});

reporters/VisualRegression

The VisualRegression reporter is responsible for creating a HTML report that reports (only) on the visual regression tests. It can be used in combination with other Intern reporters.

export reporters = [
    'Runner',
    { id: 'visual/reporters/VisualRegression', baselineLocation: './baselines', reportLocation: './reports' }
]

Contributing

We would love to hear your feedback and welcome PRs. Please take a look at Intern's Contribution Guidelines for some info and tips. Thanks!