Here is a link to a page of 108 questions that test your vocabulary, grammar, and spelling skills. The test will give you immediate feedback when you select an answer. A dialog box will pop up saying whether your answer is "정답입니다" or "정답이 아닙니다." It will also explain why the answer is right or wrong. Be careful not to confuse the "right answer" box and the "wrong answer" box because they look exactly the same, except for the words "정답입니다" and "정답이 아닙니다."
I have not finished the test, yet. I am only at Question 14, where I made my first mistake. It is not an easy test. I have only missed one so far, but I have been lucky, guessing at a couple of the answers along the way.
If anyone completes the test and would like to post your results, you can do it in the comments section of this post.