In my experience, there are certainly good and bad test-takers. Some people are more comfortable demonstrating their knowledge on a test, while others get overly-stressed and then forget everything they've learned. The best way that I can think of to accommodate all types of test takers would be to have a variety of questions and formats included in one test. For those who write best, have an short essay portion. For those who know the grammar best, have a couple questions that focus on that aspect. Along the same lines, it would also be fair to include a listening and oral part to every test to accommodate the students who excel in this portion. However, this would quickly become an extreme amount of work for the teacher, both during and outside of class, and would be extremely impractical. Because this ideal balance is simply not practical, I think tests can be slightly biased toward those who do better on written and reading segments.

I happen to be a very good test taker most of the time. I tend to do better on more objectively scored exams and worse on test that place more emphasis on essays. My ideas are not always well focused and concise, which can make answering an essay question quite difficult.

I'm not really sure what can be done to either make tests more student-friendly or to train students to be better test takers. Some might suggest that students should practice what they're worst at in an effort to improve, but I've learned that that may only make them resent it more and have it become ever more frustrating and tiresome for them.