Regression testing for styling and layout of web applications

I guess you could generate an 'ideal' shot of each page in your web application to use as reference.

Then generate a new shot of every page after a CSS update and compare with the previous ones. A 1:1 comparison should be okay if you make sure you always keep the same resolution, etc.

You could even make it so that you can tell it that if the page differs, the other page is actually 'better' than the example and to use the 'other' as the example for the next runs.

That way, when you fix something you can see the difference for one page, and mark it as being better, and then fix a bug on another page while making sure you don't regress the bug you were trying to fix in the first place.

Actually, one of the hidden gems of Selenium is that you can use it to take screen captures of the browser. Then using a technique as described in Find differences between images using C#, you can highlight the differences between previous snapshots.

This example shows how to grab a screenshot of the homepage and then create a difference image. With a little extra tinkering, you can use the same technique to count the pixels that are different.

[Test]
public void CompareHomePageToPrevious()
{
    string fileName = Path.Combine(Environment.CurrentDirectory, "homepage.bmp");
    var selenium = new DefaultSelenium("localhost", 4444, "*chrome", "http://mywebsite");
    selenium.Start();
    selenium.Open("/");
    selenium.CaptureEntirePageScreenshot(fileName, "");

    // Load current and previous captures
    var current  = new Bitmap(filename);
    var previous = new Bitmap(_previousHomepageImage);

    // Find all pixels that are the same and make them pink
    Bitmap diff = ImageTool.GetDifferenceImage(current,previous,Color.Pink);
    diff.MakeTransparent(Color.Pink);

    // Save the image for viewing
    // or count the number of different
}

Selenium is a really interesting choice because it's cross-platform and cross-browser, meaning that you can capture screens of different browsers. You can use this technique to compare snapshots between builds or to compare between browsers.

There is a way to test the layout of a web application using Galen Framework. This tool has its own language and is very easy to learn and understand. It is a Selenium-based and you can run tests in Selenium Grid, (Sauce Labs) if you want to test your application in different browsers.

This tool gets the location of a specified element on the page and check them relatively to each other.

Example: if you want to check that a menu pane is below the header and stretches to the width of a browser and has 50 pixels height, you can do it like this:

menu
    below: header 5px
    width: 100% of screen/width
    height: 50px

This tool can also be used to test responsive designs.

You can find complete documentation on the official website, http://galenframework.com.

The best part is you can even create Java tests. The Galen JavaScript API is also available along with the sample projects on GitHub.

Again, test(s) written once can be used at multiple phases of the application life cycle.