When someone attests to something, they are affirming that it is true or valid based on their personal knowledge or experience. This can involve providing a written or spoken statement, or participating in a formal process such as signing a legal document or testifying in court. Attesting can also involve providing proof of one's identity, qualifications, or competence. In general, the act of attesting is a way to establish credibility and reliability, and is often used in formal or legal contexts where accuracy and trustworthiness are essential.