A sample project with a simple implementation of BackstopJS tests that can be used by anyone who needs to run screenshot comparison tests in static web pages that have different relative URLs. E.g. http://example.com, http://example.com/page1, http://example.com/page2, etc.
To check the Node.js version installed in your computer, run
node -v. You should see something like thisv10.13.0. If you don't have Node.js installed, use the above link to download and install it.
Clone the project to your computer. Run git clone https://github.com/wlsf82/backstop-config.git.
Inside the directory of the cloned project, run npm i to install the project dependencies.
There is only one file you will have to change to get the project configured to run screenshot comparison tests for your website, which is test/basicConfig.js. Update this file by following the instructions in its comments.
If you use Windows operating system, take a look at the
NPM_SCRIPT_UPDATE_FOR_WINDOWS.mdfile.
Done. You are ready to go!
Run npm t to run the Backstop screenshot comparison tests against all the configured URLs of your website, in all the configured viewports.
Alternatively you can run the tests in a Docker container by running npm run test:docker.
Note: For Windows and Mac users, Docker needs to be installed and running. It can be downloaded from the dockerhub.
For more information about running BackstopJS tests on Docker go to the official documentation.
In the first time running the tests, it is expected that all of them fail, and an HTML report should be automatically opened for you to review the taken screenshots. It will look like the one below.
If all the screenshots represent the correct state of the website, you can approve them as bitmaps references so that next time you run the tests, new screenshots will be taken, and compared with the approved ones.
Run npm run backstop:approve to approve the bitmaps as references to be used during the screenshot comparison tests.
Re-run the tests with npm t.
After re-running the tests an HTML report like this should be available.
Done! Now every time you make changes that may affect the website visually, you can re-run the tests and get quick feedback to fix visual issues before deploying them to production.
In case of test failures due to expected visual changes in the website, remember to re-approve the new screenshots as references. Use
npm run backstop:approveto do so.
You can use git to keep track of the bitmaps reference, also references in this document as screenshots references.
To do so you just need to commit the files in the test/backstop_data/bitmaps_reference/ directory, as soon as you reviewed the screenshots, and they look good for usage in future comparisons.
Below you can see an example of the test report when BackstopJS finds a visual failure.
In case the failure is due to a real visual bug, provide a fix and continue using the same bitmaps as references (there is no need to re-approve them.)
Your feedback is very important for this project. If you have any doubts or suggestions, open an issue, and I'll look into it as soon as possible.
This is an open source project. Feel free to fork, improve it, and then create a pull request. I'll be happy to review and have it merged when it gets in a good state.
Made with 💚 by Walmyr Filho