I assume the tests would work. I'd wait and watch for fertile signs before starting to use them though. It's a bit hard to 'catch' the first ovulation before your cycles resume properly, and sometimes you get af first, then start ovulating. If you ovulate, you will have a period, unless pregnant of course.
Everyone's different - some women resume their cycles very early, despite exclusively breastfeeding, some will not ovulate until they've completely weaned, and everyone else is somewhere in teh middle. You could look into Billings for more info on tracking your fertility.