There is a test for Sabino 1, but it’s really not worth testing for since being negatives doesn’t mean not Sabino, as there are other forms not yet testable.
There are tests for SW1, 2, and 3, so it WOULD be beneficial to researchers to test for that (and it’s all under a single test), as they are still working on getting a clearer picture of whether there are small enough differences in phenotype to start to tell the different forms apart. Of course, there are horses who are sooooo obviously Splash phenotype who are not testing for 1, 2, or 3, so there are (presumably) more than 3 forms. The test is pretty new, though a lot of horses have been tested so far.