I keep wine yeast unopened for about 2 - 2 1/2 years okay.
after it has been opened i think it will keep in freezer for about 6 months if you keep it in an airtight container.
Test it by combining about 1/2 cup warm
water, maybe 110-120 deg. and a spoonfull of sugar. then add about 2 tbs of dry room temp yeast. it
should nearly double in size to a cup or so within 15 min.
Yeast is cheap so replace it if unsure.