EAB offers a range of exams that lets you test your level of proficiency in Esperanto. You don't have to be taking, or have taken, an EAB correspondence course in order to take an EAB exam; you are welcome to use the exams to complement any course of study.
For more details about the exams and rules, please see the Exams page of the Education section.
For an idea of what to expect, you can try out the specimen exam paper:
In parallel, UEA (Universala Esperanto-Asocio) operates a set of international exams, aligned to the European (Language Examinations) Reference Framework (KER): see http://edukado.net/ekzamenoj/ker/priskribo for more details about those KER international exams.
If you pass
See the pricing and buy the EAB exams online from EAB's online bookshop catalogue.
See the pricing of the KER exams from the "Kotizoj" page of edukado.net's "exams" section.
[EAB Book Service Catalogue]