The International English Language Testing System popularly known as IELTS is a standardized test conducted for non-English speakers across the globe.
Just like IELTS is used globally, for Germany you need this to enroll yourself for various English-taught programmes.
For getting into your dream English taught programme offered by your desired university, you need to appear for IELTS and score a minimum of 6.5 bands which is equivalent to B2 level. Another great reason to appear for IELTS is a profile boost that this will offer even when it is not required for German taught programmes.