A language assessment is not a pass-fail test. It is a way to determine which class would benefit you the most.
During a typical assessment we would show you a picture and ask you to describe it. Then we would ask you to listen to a recording of a 30-second conversation after which we would ask you questions about the conversation. Next, we would ask you to read a very short story about a newcomer to Canada and then ask you three questions about the story. Finally, to evaluate your writing ability, we would ask you to compare your own story as a newcomer to the story that you read.