The Celpe-Bras test is the only official language test of Brazilian portuguese, as far as I know. It is required if you want to revalidate your foreign university diploma here in Brazil, which I recommend to anyone who plans to stay here for the long-term, teach at a local university, do a "mestrado" or PhD program here, or exercise a profession for which there are special requirements (bar exam for lawyers, membership in a professional association). The test is only administered twice a year (usually in April and October), and the request for revalidation can also be done only twice a year (in February and August). As a consequence, the whole process of revalidating your diploma can take more than a year and it is advisable to do the language test soon.
The next Celpe-Bras test will be in October and the deadline for enrolling is until August 29th. Please find below the link with further information. Very oddly, I could not find a place to do the test in Sao Paulo, although all major Brazilian cities are covered. I will do it a the UNICAMP in Campinas where it costs Protected content .