I note our private HS with high-level college counseling services generally recommends students take both a relatively early SAT and relatively early ACT to figure out which is best for them. The students then have time to take up to two more of their favorite as warranted (they generally recommend strongly against taking more than at most three of one test). Of course if your first early test goes well enough, you could abandon the other early test, or indeed be entirely done.
“Early” SATs would include the December and March dates of Junior year. “Early” ACTs would include the December and February dates. Two in December is a lot, so in practice this can mean doing the February ACT and then either the December or March SAT.
This is definitely not something you must do. But the logic of figuring out your best test in time to do focused prep and possibly one more retake for that test makes some sense.