The Compass Prep guide has all the testing dates and college testing requirements and will help you figure out a strategy for getting all the tests you need junior year. If possible, save fall of senior year for retakes only.
If the university “recommends” subject tests, then I would consider that to mean “required.” Otherwise, your child could be and probably will be at a disadvantage during admissions.
I’m relaying information that I’ve gathered from attending speakers, counselors, meetings, seminars, etc. over the past two years (D’s sophomore and junior years) at a public high school with ALL socio-economic levels and a VERY diverse student population.