Teacher testing as a prerequisite to professional employment has a long history in the United States, and while exact requirements vary from state to state, testing as a licensure requirement is ubiquitous. This presentation explores the landscape around teacher testing in mathematics, highlighting two trends in how teachers’ readiness is assessed and how these assessments have shifted over time. One important trend is a shift from measuring only teachers’ content knowledge of mathematics to additionally measuring their mathematical knowledge for teaching (MKT). A second trend is the move toward measuring practical competencies through performance measures, which has accompanied a larger shift in programs of teacher preparation to focus on what teachers do rather than just on what they know. A focus on MKT over traditional content can be seen as pushing back on long-held assumptions about what teachers need to know. A focus on performance values what teachers are able to do with their knowledge, pushing us as a field toward consensus around what constitutes a ‘safe to practice’ standard. Both represent significant changes from historical trends that focused on direct measures of the curricular content, and offer the potential for closer links between what is tested and what is emphasized in teacher preparation programs.