#BackstopJS Catch CSS curve balls.

BackstopJS automates CSS regression testing of your responsive web UI by comparing DOM screenshots at various viewport sizes.

Try the step-by-step tutorial on css-tricks.com.

Learn more at http://BackstopJS.org/.

##Heres how it works:

1. Set up a test config file: specify screen sizes and DOM selectors.
2. Use BackstopJS to create reference screenshots.
3. Make some changes to your CSS or add new DOM components.
4. Run a test. BackstopJS creates a set of test screenshots and any changes show up in a report!

##Backstory: BackstopJS is basically a wrapper around the very fabulous Resemble.js component written by James Cryer. Other implementations of Resemble.js, namely PhantomCSS require writing long form CasperJS tests. This is of course great for testing complex UI interactions – but kind of cumbersome for more simple applications like static CMS templates or other higher level sanity testing.

BackstopJS may be just the thing if you develop custom Wordpress, Drupal or other CMS templates. Tested on OSX.

BackstopJS was created by Garris Shipon at Art.com labs.

Follow @garris

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##Installation

BackstopJS package

You can add BackstopJS from the root directory of any project.

$ bower install backstopjs

This will create the folder structure <root>/bower_components/backstopjs.

Install NPM dependencies

$ cd bower_components/backstopjs
$ npm install

If you don't already have a global Gulp instance... http://gulpjs.com

$ sudo npm install gulp -g

If you don't already have a global PhantomJS install... http://phantomjs.org/download.html

$ npm install phantomjs

If you don't already have a global CasperJS install... http://docs.casperjs.org/en/latest/installation.html

$ npm install -g casperjs

##Configuration

If you don't already have a BackstopJS config file. The following command will create a config template file which you can modify in your root directory. Note: this will overwrite any existing backstopjs config file.

From the bower_components/backstopjs directory.

$ gulp genConfig

From the project root, see ./backstop.json

If that file is not present then the following file is used... bower_components/backstopjs/capture/config.default.json

{
	"viewports" : [
		{
		 "name": "phone",
		 "viewport": {"width": 320, "height": 480}
		}
		,{
		 "name": "tablet_v",
		 "viewport": {"width": 568, "height": 1024}
		}
		,{
		 "name": "tablet_h",
		 "viewport": {"width": 1024, "height": 768}
		}
	]
	,"grabConfigs" : [
		{
			"testName":"http://getbootstrap.com"
			,"url":"http://getbootstrap.com"
			,"hideSelectors": []
			,"removeSelectors": [
				"#carbonads-container"
			]
			,"selectors":[
				"header"
				,"main"
				,"body .bs-docs-featurette:nth-of-type(1)"
				,"body .bs-docs-featurette:nth-of-type(2)"
				,"footer"
				,"body"
			]
		}
	]
}

##Usage

generating (or updating) reference bitmaps

From the bower_components/backstopjs directory.

$ gulp reference

This task will create a (or update an existing) bitmaps_reference directory with screen captures from the current project build.

generating test bitmaps

From the bower_components/backstopjs directory.

$ gulp test

This task will create a new set of bitmaps in bitmaps_test/<timestamp>/.

Once the test bitmaps are generated, a report comparing the most recent test bitmaps against the current reference bitmaps will run. Significant differences will be detected and shown.

troubleshooting

BackstopJS is fairly bare bones and there is not much in the way of guardrails to recover from things like an invalid config or a file not found. If something goes wrong it generally manifests in casperJS complaining about a missing selector. If this happens you have the option of sending the configured URL(s) file contents to the console.

From the bower_components/backstopjs directory.

$ gulp echo

This is probably the best way to troubleshoot -- from here you can verify that PhantomJS is indeed making a successful file query (and receiving the correct file back too.)

Usage Notes

dynamic content

For obvious reasons, this screenshot approach is not optimal for testing live dynamic content. The best way to test a dynamic app would be to use a known static content data stub – or ideally many content stubs of varying lengths which, regardless of input length, should produce certain specific bitmap output.

That said, for a use case where you are testing a DOM with say an ad banner or a block of dynamic content which retains static dimensions, we have the hideSelectors property in capture/config.json which will set the corresponding DOM to visibility:hidden, thus hiding the content from our Resemble.js analysis but retaining the original layout flow.

"hideSelectors": [
	"#someFixedSizeDomSelector"
]

There may also be elements which need to be completely removed during testing. For that we have removeSelectors which sets elements to display:none.

"removeSelectors": [
	"#someUnpredictableSizedDomSelector"
]

running the report server

The test comparison report was written in Angular.js and requires a running HTTP server instance. This instance is auto-started after a test is run. The server is also auto-stopped after 15 minutes so you don't have to go worrying about bloaty node processes running all over the place.

To manually start the server... from the bower_components/backstopjs directory.

$ gulp start

...and to manually stop there is... from the bower_components/backstopjs directory.

$ gulp stop

fin.