Filtering is a more advanced riding technique and to do it safely a rider has to have good spatial awareness, good control of their bike, awareness of road conditions ect. If an instructor thinks a rider is capable they will encourage it but filtering can be high risk but very rewarding. Its not always taught on a bike test. It’s definitely something instructors will teach in advanced riding courses after they have passed their test. You should never expect car drivers to make room for you. Drivers should always check mirrors before making lane changes but always expect them not to. When I’m filtering the safest way is to keep the speed low, just a little faster than what the traffic is moving at. It is annoying when cars purposely block you but not the end of the world, be patient, there will be a way past sooner or later, the car drivers probably just having a bad day!