There's no single "IB entrance test." The difficulty of any IB admissions test depends heavily on the specific school and the type of test they administer. Some schools might not have any formal entrance exam at all, relying instead on prior academic records and interviews. Others might use standardized tests like the SSAT or ISEE, which are widely used for private school admissions and have varying difficulty levels depending on the grade level. Still others may design their own tests, focusing on specific skills or subject matter relevant to their IB program.
Therefore, it's impossible to give a blanket "easy" or "difficult" answer. Some entrance assessments might be relatively straightforward for well-prepared students, while others could be quite challenging. The best way to determine the difficulty is to contact the specific IB school you're interested in and inquire about their admissions process and the nature of any assessments they use.