The Spanish verb 'testar' comes from the Latin verb 'testari', meaning 'to testify or bear witness'. This Latin verb was derived from 'testis', meaning 'witness'. The evolution from bearing witness to making a will makes sense historically, as the act of making a will inherently involves declaring or testifying one's final wishes in the presence of witnesses. The secondary meaning 'to test' developed from the idea of examining or verifying something, similar to how a witness would verify facts.

Several common Spanish words share this Latin root, including 'testigo' (witness), 'testimonio' (testimony), and 'testamento' (testament/will). All these words preserve the core concept of witnessing, verifying, or declaring something officially.

English speakers can easily connect 'testar' to several familiar English words that come from the same Latin root: 'test', 'testify', 'testimony', 'testament', and 'attest'. Just as 'testar' involves verifying (testing) or making official declarations (as in a will), these English words all relate to proving, verifying, or making formal statements.