To obtain an official certificate of your level, you have to sit a DELF (A1-B2) or DALF (C1-C2) exam in person. There are plenty of unofficial tests online that you can use to gauge your level, such as:
1. https://delfdalf.ch/index.php?id=292&no_cache=1
2. http://www.languagelevel.com/french/
3. http://www.french-exam.com/mock-french-exam/
Bonne chance!