Was it necessary before changing lanes at the intersection to make sure that it was safe?

Why?

Every lane change requires particular care and a check that it can be made safely, including during a turn. The video shows a black car travelling on your right, whose position you must consider before moving over. Check your mirrors and blind spot, and give way to a vehicle already travelling in the lane you intend to enter.

art. 22 ust. 1 i 4 Prawa o ruchu drogowym