If you want to check the implementation status of CSS Blend Modes in the browser you are using (or targeting), you can now easily do so by looking at the CSS Blend Modes Browser Support Matrix.
When creating this matrix, we took advantage of the awesome work done for CSS Regions. In fact, we used the same code, so behind the scenes, the support matrix uses QUnit for unit tests and BrowserScope for storage. The only significant change to the backend is the addition of a manual testing capability.
Not adding manual tests would limit the testing to whether the related CSS properties are considered valid by the browser, and that would have left a large area of the feature uncovered. False positives could ensue. (e.g. at the moment, in some browsers only the parsing of mix-blend-mode is implemented; the property is valid, the automated tests pass, but no blending actually takes place).
We tried to make the manual testing experience as painless as possible. The tests are simple, and are integrated in the same QUnit suite that runs the automated tests (via asyncTest). To avoid unnecessary testing, when a specific property parsing test fails, related manual tests will not be displayed, and their results will be registered as failures.
As the implementation progresses, we will keep the matrix updated with the latest support. That is, within reasonable limits – we will do it for major releases, but not after every patch that gets submitted. Of course, if you want up to date information on a nightly build, or for some reason are unhappy with what you see in the submitted results, you can always run the tests in the browser yourself. Just don’t forget to enable the appropriate flag before you do. You can also check out the sources on github.
In learning from its CSS Regions predecessor, to keep the matrix clean, the results submission mechanism will not be available externally. The Regions matrix initially went for a crowdsourcing approach, but a few months in the ‘internet’ wild proved that to be ‘suboptimal’.
The testing currently covers the background-blend-mode, mix-blend-mode and isolation (parsing) CSS properties and the Canvas 2D globalCompositeOperation attribute. Support for testing SVG blending will be added in the future.