An attestation engagement is one in which a CPA is engaged to Assemble pro forma financial statements based on the representations of the entity's management without expressing any assurance. Issue a written communication expressing a conclusion about the reliability of a written assertion that is the responsibility of another party. Provide tax advice or prepare a tax return based on financial information the CPA has not audited or reviewed. Testify as an expert witness in accounting, auditing, or tax matters, given certain stipulated facts.