In the technical jargon employed by notaries public in Spain, a “testimonio” is just a certified copy of a notarial deed. In the case given, a deed of sale has been issued by a notary, as you, asker, describe. Its “testimonio” is just a certified copy of that deed produced by the notary public, certainly intended for the buyer themselves.

Ah, there is nothing wrong with the missing full stop at the end of that excerpt. That is nothing rare, unluckily, in such type of documentation…

https://dle.rae.es/testimonio
testimonio
2. m. Documento autorizado por funcionario público [in this case: Notary public], en el que se da fe de un hecho o se transcribe total o parcialmente el contenido de otro documento.