@skieurope is correct. You don’t need an AP course to take subject tests. It can be easier to prepare for the subject tests if you take it at the same time you are finishing an AP class. My son took APUSH and AP Chem and had the AP exams and subject tests within a week of each other. Since he was already studying for the AP exams there was minimal extra studying. He spent time familiarizing himself with the format of the tests but he was already up to speed on the content.