This article discusses the importance of assessment in STEM education and provides guidelines for developing and evaluating assessments. It emphasizes the need for robust assessments in daily instruction, research, and evaluation in STEM fields. The article also highlights the importance of grounding assessments in claims and evidence, and the role of validity in interpreting and using test results. It offers guidance for the use of quantitative assessments and recommends evaluating tests based on professional judgment, validity evidence, available alternatives, and applicable guidelines/laws. The article introduces a project called Validity and Measurement in Mathematics Education (V-M2Ed) that aims to create a repository of quantitative mathematics tests and assessments. It also emphasizes the importance of validation research as equity-forward scholarship and encourages assessment scholars to promote equity in their work. Overall, the article provides a brief overview of modern assessment theory and offers insights for future learning and research in the field.