Having just graduated with a BS in CS, I think that I can sum this one up for you in one word: nothing.
I went into computer science at Oregon State University with a passion for games and computers (originally I thought the degree would help me get a network admin job, until I realized I didn't want that job). Four years later I graduated with a 3.01 cumulative gpa and more knowledge about software that I could possibly hope to remember.
In your first two years you will not be expected to know anything about programming and the teachers will give you the fundamentals. After that your instructors will expect that you know the basics and will push just how fast you can learn. Expect many long nights trying to learn and accomplish a programming assignment.
As for your testing, most colleges should have facilities that can help you, since it just sounds like you have trouble taking tests. Don't worry though, in CS you're more likely to be graded on your projects than your tests, although testing well will still be important.