A more thorough explanation:

Definition: Attest means to testify or confirm that something is true, genuine, or authentic.

For example, in a legal context:

• Evidence law: To "attest" means to certify the verity of a copy of a public document formally by signature. An attested copy of a document is one that has been examined and compared with the original, with a certificate or memorandum of its correctness, signed by the persons who have examined it.
• Wills: The term "attest" means the act of witnessing the performance of statutory requirements as to the valid execution of a will and doing things that the statute requires the witness to do as part of attestation.

These examples illustrate how attest is used in a legal context to confirm the authenticity of a document or the validity of a will. Attesting to something means that you are providing evidence or testimony that supports its truth or genuineness.