- Website: http://responsivenews.co.uk
- Source: http://github.com/bbc-news/wraith
Selenium-Wraith is an augmentation of the BBC Wraith gem by Andrew Tekle-Cadman of Future Visible Ltd.
The original Wraith is a screenshot comparison tool, created by developers at BBC News, for headless browser url-based comparison of responsive web sites.
Wraith uses either PhantomJS or SlimerJS to create screen-shots of different environments and then creates a diff of the two images, the affected areas are highlighted in blue.
Selenium-Wraith draws heavily on the Wraith gem, forking the Wraith repo at the GitHub commit 88c5db7.... on 16/4/2014. It retains all the Wraith functionality up to that point but also greatly increases it's capabilities.
Selenium-Wraith adds the following capabilities to Wraith
- Selenium integration, both running locally on a desktop or on a selenium grid
- Browser to browser screenshot comparison
- Page component-based comparison
In general code has been added or changed within the original Wraith classes. A new driver code module has also been added.
The addition of the new functionality to the Wraith gem has added considerable complexity to the code base. In order to keep the code maintainable, over 100 RSpec unit tests have been added and a single Cucumber BDD scenario outline with 6 examples. The original Wraith tests have been deleted.
Each cucumber scenario covers a major area of functionality, although necessarily these overlap considerably. Each use their own test configuration file located in /spec/resources/configs, which are copies of the config files in the templates folder. The central idea behind the creation of these scenarios is both to maintain the Wraith-Selenium code but also to help properly document the greatly expanded number of configuration options.
Most but not all of the cucumber scenarios can run simultaneously. However some, such as the scenario for running a selenium grid, necessarily rely on a different initial set up and must be run in isolation. This should be born in mind by commenting out the incompatible examples when running the scenarios.
In order to best document the powerful configuration options in Selenium-Wraith, a number of sample configuration files are present in the templates directory. Each file contains extensive comments.
These are:
#phantomjs_local_url_page_desktop_config.yaml Ued for running the pre-existing Wraith functionality using phantomJS.
#selenium_grid_browser_page_desktop_config.yaml Used for running browser-based comparison on a selenium grid.
#selenium_local_browser_component_desktop_config.yaml Used for running selenium locally using locally installed desktop browsers (chrome,safari) with browser-based comparison and testing page components rather than whole pages.
#selenium_local_url_page_desktop_config.yaml Used for running selenium locally using locally installed desktop browsers with url-based comparison.
#selenium_local_url_page_device_config.yaml Used for running selenium locally and testing locally attached devices (in this case an iPad 2 attached to a Mac Pro machine) with url-based comparison.
You can run selenium locally, using a combination of local browsers on the 'desktop', against locally attached 'devices' or a combination of the two. If running a browser as a device then as you would expect you need to configure the URL to copy of webdriver running on the device and the precise device name. See the example config files in /spec/resources/configs for details.
Running in grid mode gives you the usual basic selenium capabilites, including the ability to pass multiple different browser versions and platforms to the grid for management.
As with the original Wraith gem, details of the environment used to capture each screenshot (browser, browser platform, platform as so on, is preserved in the screen shot file name and thumbnail file name and later parsed for use in the gallery.
Selenium was found to have a few idiosyncracies, most notably the different way it interpretes browser width for different browsers. This cause some issues with browse-based comparison (see below for discussion).
Wraith used url-based comparison. That is, screenshots taken of different urls from the same browser could be compared against each other. This is ideal for, say, comparing web sites in different test environments.
Wraith-Selenium retains this functionality but also adds browser-based comparison. Browser-based comparison is necessary to minimise the substantial overhead of development and testing teams checking a web site between different browsers and browser versions.
Unfortunately, Selenium interpretes browser width different according to browser, browser version and even the width stipulated. This means that the first time you run a browser-based comparison, some of the diff images produced may be invalid as diffs can only be done on screenshots on identical size. To overcome this, you must manually inspect the widths of the screenshots produced and add a bias term in the config file. See the test configuration files for further details.
Browser-based comparison is a one-to-many rather than one-to-one comparison relationship, and this has necessitated the rewriting of how file comparison is done. For one thing, file crops do not now overwrite the original screenshot but are stored in a separate directory for later access. The reason for this is that one base file may have to be cropped to several different sizes to compare against different comparison files.
The default behaviour using Wraith is to load a page and change the page width in order to check responsive design.
However, in many cases it may be required just to check the responsiveness of a page component rather than the whole page itself.
It is possible in Wraith-Selenium to change the page origin and dimensions of the page, thereby allowing several different components on a single page to be screen shot and then compared either on a different url or a different browser basis.
At the time of writing this functionality is fairly immature, having been successfully tested only in chrome and safari. It is known not to work in firefox due to the different way Firefox handles screenshots, and a workaround at the cropping stage will almost certainly be necessary in order to rectify this.
Installing and running Selenium-Wraith is very similar to the original BBC Wraith gem. The documentation below is taken from the BBC Wraith gem README file.
Open terminal and run
gem install wraith
You can then run the following to create a template snap.js and config file:
wraith setup
You can type wraith into terminal to bring up the list of commands, but the one to start Wraith is
wraith capture config_nameThis assumes that your snap.js and config.yaml are in the folders that were created on setup. There are other commands also available, these all expect a config_name to be passed as an option. Wraith will look for the config file at configs/[config_name].yaml.
wraith capture config_name # A full Wraith job
wraith compare_images config_name # compares images to generate diffs
wraith crop_images config_name # crops images to the same height
wraith setup_folders config_name # create folders for images
wraith generate_gallery config_name # create page for viewing images
wraith generate_thumbnails config_name # create thumbnails for gallery
wraith reset_shots config_name # removes all the files in the shots folder
wraith save_images config_name # captures screenshots
wraith setup # creates config folder and default configAfter each screenshot is captured, the compare task will run, this will output a diff.png and a data.txt. The data.txt for each file will show the number of pixels that have changed. There is a main data.txt which is in the root of the output folder that will combine all of these values to easier view all the pixel changes.
A gallery is available to view each of the images and the respective diff images located in the shots folder once all the images have been compared.
##Running Tests
Both Rspec and Cucumber tests are designed to run using the /spec/resources as the working directory.
To run the cucumber features:
cucumber --color -r ../../cucumber-bdd/features
The tests will not work correctly unless the working directory is properly set, as they rely on accessing and creating files and folders beneath this root.
If you want to add functionality to this project, pull requests are welcome.
- Create a branch based off master and do all of your changes with in it.
- If you have to pause to add a 'and' anywhere in the title, it should be two pull requests.
- Make commits of logical units and describe them properly
- Check for unnecessary whitespace with git diff --check before committing.
- If possible, submit tests to your patch / new feature so it can be tested easily.
- Assure nothing is broken by running all the test
- Please ensure that it complies with coding standards.
Please raise any issues with this project as a GitHub issue.
The original BBC Wraith gem is available to everyone under the terms of the Apache 2.0 open source license. Selenium-Wraith follows this licensing model. Take a look at the LICENSE file in the code.
Original Wraith Gem
Selenium-Wraith
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