Good question. I'm not going to quite call this one an errata - almost, but not quite.
I have, however added a note to clarify the question in the mock exam.
In general, the questions on the real exam will tell you what you need to know, and in this case the question would have said that assertions were enabled. On the other hand, the general rule for the real exam is that if something is not stated explicitly, assume it's working. So things like correct compilers and JVMs and classpaths and imports, and command line invocations and stuff should be assumed to be correct if they're not listed explicitly on the question.
So for instance, if you see a code snippet without the entire class listed, you can assume the import statements are correct.
On the other hand, if you see a complete class listing and you think an import statement is missing, that might be the key to the question.
Does that make sense?