Hi there!

The AP does indeed have “subject tests” in that there are exams available for each subject. In the US, these exams are typically given in May at the end of a school year; students can take these exams at the end of taking the relevant course in school, or if the school doesn’t offer an AP curriculum or a particular AP course, students can self-study for the AP exam and sign up for the exam independently. More information on the AP can be found on the official AP’s page: https://apstudent.collegeboard.org/home

However, you bring up another interesting point! Students can also take SAT subject tests to show mastery of a subject. Yes, many students choose not to take the SAT reasoning test and choose to take the ACT exam instead, also taking the SAT subject tests. Many colleges offer this combination (ACT with writing and SAT subject tests) to fulfill their standardized testing requirements, but check with each school to make sure they don’t have any additional requirements, as schools vary.

Hope this helps!