The trend over the last 3 years has been for colleges to drop the ACT / SAT writing test requirement. Stanford, Michigan, Dartmouth, Harvard, Brown, U. San Diego among many others have all dropped this testing requirement in recent years.
OTOH the University of California still requires it. Check with each individual college.
Note also that most of the highly selective colleges that have dropped the requirement have replaced it with a much more rigorous version fo a writing assessment: submission of an actual graded essay as part of the admissions packet.
So in reality, if you're aiming high and want to be admitted to a selective school, they care intensely about your writing ability and will find one way or another to assess it. You'd be best advised to improve your skill at writing clear, cogent, analytical prose regardless of whether you take the writing test or not... so why not just take the writing test anyway?