Regression testing for styling and layout of web applications

Question

I realise this is a non-trivial task, but is there a way to regression test the styling and rendered layout of a web application?

I\'ve found it straightforward to unit t

Answer 1

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.