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Automating Page Actions

Taking screenshots of specific sections of the page is a powerful feature, even if it requires a little more effort. But what happens when the screenshot you need is hidden behind some sort of action (e.g. a mouse click to open a modal window)?

Lucky, PhantomCSS is tied directly in to CasperJS/PhantomJS, so all of the functionality of those two frameworks is available for use.

What are PhantomJS and CasperJS?

Officially, PhantomJS is a “headless WebKit engine”. In simpler terms, PhantomJS is a browser that’s built for testing and automation. It does almost everything a regular browser does, but behind the scenes. “Headless” comes from the fact that it doesn’t have a visual interface. All interaction takes place via scripts.

CasperJS comes in to help with scripting. According to its website:

It eases the process of defining a full navigation scenario and provides useful high-level functions, methods & syntactic sugar for doing common tasks.

In other words, it makes working with PhantomJS easier.

PhantomCSS ties in to both of these to provide a very functional suite of tools.



  1. Open the ‘Add-ons’ style guide page in your browser for reference.
  2. In your editor, open the ‘phantom-addons.js’ file.
  3. Again, add the function to start CasperJS immediately after the ‘Tests go here’ comment. Be sure to have it load the ‘addons.html’ page.
  4. Since we need to first open the modal, we’ll use CasperJS to trigger the click. In a new then callback, use the click function to click the link inside the “Here’s a simple modal dialog” sentence.
  5. The modal animates open, so we need to wait for the animation to finish before capturing a screenshot. We could set a timeout, but there’s a better way. Using Casper’s ‘waitForSelector’ function, add a wait for the fancybox-opened class to appear on the fancybox-wrap class/container.
  6. Inside of the ‘waitForSelector’ callback function, add you PhantomCSS screenshot command for the .fancybox-wrap class.
  7. Now you’re ready to run your tests. Use casperjs test phantom-addons.js to try out your script.
  8. Validate it generated the right screenshot by checking the ‘ex-4-screenshots’ folder.
  9. Add a bottom margin of 1em on the .page-title class in your CSS (in the main.css or _common.scss file).
  10. Run your tests again and see if it catches the difference.

Extra Credit

We’re testing a responsive starter kit framework, so how do we take screenshots at multiple resolutions? While not built-in to PhantomCSS like Wraith, since they both use PhantomJS behind-the-scenes, you can achieve the same end. Follow Adnane Belmadiaf’s tutorial and try capturing screenshots at 320px and 1024px.


There’s a wealth of functionality that PhantomJS/CasperJS provide. By having our UI regression testing tool tied in to it, we can create very complex scenarios to validate our UI.

Further Reading


Step 3


Step 4

casper.then(function () {'a[href="#modal-content"]');

Step 5

casper.waitForSelector('.fancybox-opened.fancybox-wrap', function () {


Step 6

casper.waitForSelector('.fancybox-opened.fancybox-wrap', function () {
    phantomcss.screenshot('.fancybox-wrap', 'Modal Overlay');